You will be given a definition of a task first, then some input of the task.
In this task, you're given passages that contain mentions of names of people, places, or things. Some of these mentions refer to the same person, place, or thing. Your job is to write questions that evaluate one's understanding of such references. Good questions are expected to link pronouns (she, her, him, his, their, etc.) or other mentions to people, places, or things to which they may refer. Do not ask questions that can be answered correctly without understanding the paragraph or having multiple answers. Avoid questions that do not link phrases referring to the same entity. For each of your questions, the answer should be one or more phrases in the paragraph, and it should be unambiguous.

Passage: Mountains dominate central and western Rwanda. They are part of the Albertine Rift Mountains that flank the Albertine branch of the East African Rift, which runs from north to south along Rwanda's western border. The highest peaks are found in the Virunga volcano chain in the northwest; this includes Mount Karisimbi, Rwanda's highest point, at 4,507 metres (14,787 ft). This western section of the country lies within the Albertine Rift montane forests ecoregion. It has an elevation of 1,500 to 2,500 metres (4,921 to 8,202 ft). The centre of the country is predominantly rolling hills, while the eastern border region consists of savanna, plains and swamps.Rwanda has a temperate tropical highland climate, with lower temperatures than are typical for equatorial countries because of its high elevation. Kigali, in the centre of the country, has a typical daily temperature range between 12 and 27 °C (54 and 81 °F), with little variation through the year. There are some temperature variations across the country; the mountainous west and north are generally cooler than the lower-lying east. There are two rainy seasons in the year; the first runs from February to June and the second from September to December. These are separated by two dry seasons: the major one from June to September, during which there is often no rain at all, and a shorter and less severe one from December to February. Rainfall varies geographically, with the west and northwest of the country receiving more precipitation annually than the east and southeast. Global warming has caused a change in the pattern of the rainy seasons. According to a report by the Strategic Foresight Group, change in climate has reduced the number of rainy days experienced during a year, but has also caused an increase in frequency of torrential rains. Both changes have caused difficulty for farmers, decreasing their productivity. Strategic Foresight also characterise Rwanda as a fast warming country, with an increase in average temperature of between 0.7 °C to 0.9 °C over fifty years.
Output:
What is the name of the country in which the center is predominantly rolling hills while the eastern border region consists of savanna, plains and swamps?