请教一题PREP SC

81. Both the caribou and the reindeer belong to the species Rangifer tarandus, but after 7,000 years of domestication in Eurasia, reindeer have developed a tendency to circle in tight groups, while caribou tend to spread far and wide.

(A) belong to the species Rangifer tarandus, but after 7,000 years of domestication in Eurasia, reindeer have developed a tendency to circle in tight groups, while caribou tend

(B) belong to the same species, Rangifer tarandus, but about 7,000 years of domestication in Eurasia have developed reindeer's tendency to circle in tight groups, which is different from caribou that tend

(C) belong to the species Rangifer tarandus, but being domesticated in Eurasia for about 7,000 years has developed reindeer's tendency to circle in tight groups, and that is different from caribou tending

(D) are the same species, Rangifer tarandus, but about 7,000 years of domestication in Eurasia have developed reindeer's tendency to circle in tight groups, while the tendency is for caribou

(E) are the same species, Rangifer tarandus, but being domesticated in Eurasia for about 7,000 years has developed the reindeer's tendency to circle in tight groups, which differs from caribou tending

答案是A。但我觉得A有问题：after 7,000 years of domestication in Eurasia, reindeer have developed a tendency to circle in tight groups, while caribou tend

1 为什么要用完成时态

2 为什么while前用完成时态，while后面却不用完成时态

3 reindeer应该用has ， 还是have