You will be given a definition of a task first, then some input of the task.
In this task, you are given a context, a subject, a relation, and many options. Based on the context, from the options select the object entity that has the given relation with the subject. Answer with text (not indexes).

Context: Infantry is the general branch of an army that engages in military combat on foot. As the troops who engage with the enemy in close-ranged combat, infantry units bear the largest brunt of warfare and typically suffer the greatest number of casualties during a military campaign. Historically, as the oldest branch of the combat arms, the infantry are the tip of the spear of a modern army, and continually undergo training that is typically more physically demanding and psychologically stressful than that of any other branch of the combat arms. Common representations of infantry fighting forces include the U.S. Army Infantry Branch, U.S. Marine Corps Infantry, Royal Canadian Infantry Corps, Infantry of the British Army, and the Royal Australian Corps of Infantry., Fortifications are military constructions or buildings designed for the defense of territories in warfare, and also used to solidify rule in a region during peace time. Humans have constructed defensive works for many thousands of years, in a variety of increasingly complex designs. The term is derived from the Latin "fortis" ("strong") and "facere" ("to make")., Self-propelled artillery (also called mobile artillery or locomotive artillery) is artillery equipped with its own propulsion system to move towards its target. Within the term are covered self-propelled guns (or howitzers) and rocket artillery. They are high mobility vehicles, usually based on continuous tracks carrying either a large howitzer, field gun, a mortar or some form of rocket or missile launcher. They are usually used for long-range indirect bombardment support on the battlefield., A siege is a military blockade of a city or fortress with the intent of conquering by attrition or assault. This derives from "sedere", Latin for "to sit". Siege warfare is a form of constant, low-intensity conflict characterized by one party holding a strong, static defensive position. Consequently, an opportunity for negotiation between combatants is not uncommon, as proximity and fluctuating advantage can encourage diplomacy., Artillery is a class of large military weapons built to fire munitions far beyond the range and power of infantry's small arms. Early artillery development focused on the ability to breach fortifications, and led to heavy, fairly immobile siege engines. As technology improved, lighter, more mobile field artillery developed for battlefield use. This development continues today; modern self-propelled artillery vehicles are highly mobile weapons of great versatility providing the largest share of an army's total firepower., A siege engine is a device that is designed to break or circumvent city walls and other fortifications in siege warfare. Some have been operated close to the fortifications, while others have been used to attack from a distance. From antiquity, siege engines were constructed largely of wood and tended to use mechanical advantage to fling stones and similar missiles. With the development of gunpowder and improved metallurgical techniques, siege engines became artillery. Collectively, siege engines or artillery together with the necessary troops and transport vehicles to conduct a siege are referred to as a siege-train., In international arms control, small arms include revolvers and pistols, rifles and carbines, assault rifles, submachine guns and light machine guns. Together with light weapons (heavy machine guns; hand-held grenade launchers; portable anti-aircraft and anti-tank guns; recoilless rifles; portable launchers of anti-aircraft and anti-tank missile systems; and mortars of calibres of less than 100 mm), they comprise the Small Arms and Light Weapons (SALW) protocol., Field artillery is a category of mobile artillery used to support armies in the field . These weapons are specialized for mobility , tactical proficiency , long range , short range and extremely long range target engagement . Until the early 20th century , field artillery were also known as foot artillery , for while the guns were pulled by beasts of burden ( often horses ) , the gun crews would usually march on foot , thus providing fire support mainly to the infantry . This was in contrast to horse artillery , whose emphasis on speed while supporting cavalry units necessitated lighter guns and crews riding on horseback . Whereas horse artillery has been superseded by self - propelled artillery , field artillery has survived to this day both in name and mission , albeit with motor vehicles towing the guns , carrying the crews and transporting the ammunition . Modern artillery has also advanced to rapidly deployable wheeled and tracked vehicles and precision delivered munitions capable of striking targets at ranges between 15 and 300 kilometers ., Subject: field artillery, Relation: has_part, Options: (A) a (B) artillery (C) engine (D) field (E) field gun (F) infantry (G) infantry corps (H) light (I) one (J) system (K) technology (L) train
Output:
field gun