The valley of mexico has an elevation of 7000 feet. how can it be a valley and still be so high above sea level

The Valley of Mexico, or the Mexican Plateau, is on a very high elevation for a valley, around 7,000 feet. The reason why it can be considered as a valley in way is the surrounding relief. Despite it being so high, the valley is actually surrounded on the west, east and south by higher relief forms, the three mountain ranges that are higher that it, so it seems like a valley compared to them. In theory it is actually a plateau, but considering the climate zone i  which it is located, this plateau actually has all the characteristics of a nice, large, fertile valley.

the answer is b for brother