In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

Waves contain?, Context: As an electro-magnetic wave travels through the different parts of the antenna system (radio, feed line, antenna, free space) it may encounter differences in impedance (E/H, V/I, etc.). At each interface, depending on the impedance match, some fraction of the wave's energy will reflect back to the source, forming a standing wave in the feed line. The ratio of maximum power to minimum power in the wave can be measured and is called the standing wave ratio (SWR). A SWR of 1:1 is ideal. A SWR of 1.5:1 is considered to be marginally acceptable in low power applications where power loss is more critical, although an SWR as high as 6:1 may still be usable with the right equipment. Minimizing impedance differences at each interface (impedance matching) will reduce SWR and maximize power transfer through each part of the antenna system.
power

Why do birds possess gizzards?, Context: Like the reptiles, birds are primarily uricotelic, that is, their kidneys extract nitrogenous waste from their bloodstream and excrete it as uric acid instead of urea or ammonia through the ureters into the intestine. Birds do not have a urinary bladder or external urethral opening and (with exception of the ostrich) uric acid is excreted along with feces as a semisolid waste. However, birds such as hummingbirds can be facultatively ammonotelic, excreting most of the nitrogenous wastes as ammonia. They also excrete creatine, rather than creatinine like mammals. This material, as well as the output of the intestines, emerges from the bird's cloaca. The cloaca is a multi-purpose opening: waste is expelled through it, most birds mate by joining cloaca, and females lay eggs from it. In addition, many species of birds regurgitate pellets. Males within Palaeognathae (with the exception of the kiwis), the Anseriformes (with the exception of screamers), and in rudimentary forms in Galliformes (but fully developed in Cracidae) possess a penis, which is never present in Neoaves. The length is thought to be related to sperm competition. When not copulating, it is hidden within the proctodeum compartment within the cloaca, just inside the vent. The digestive system of birds is unique, with a crop for storage and a gizzard that contains swallowed stones for grinding food to compensate for the lack of teeth. Most birds are highly adapted for rapid digestion to aid with flight. Some migratory birds have adapted to use protein from many parts of their bodies, including protein from the intestines, as additional energy during migration.
contains swallowed stones for grinding food to compensate for the lack of teeth

What position did Nasser hold?, Context: Nasser was known for his intimate relationship with ordinary Egyptians. His availability to the public, despite assassination attempts against him, was unparalleled among his successors. A skilled orator, Nasser gave 1,359 speeches between 1953 and 1970, a record for any Egyptian head of state. Historian Elie Podeh wrote that a constant theme of Nasser's image was "his ability to represent Egyptian authenticity, in triumph or defeat". The national press also helped to foster his popularity and profile—more so after the nationalization of state media. Historian Tarek Osman wrote:
head of state