过去时和完成时的区别!Insects first appeared 400 million years ago.Down thro_英语解答

过去时和完成时的区别!
Insects first appeared 400 million years ago.Down through the ages,they ____endlessly to survive.
A.struggled B.have struggled

人气：473 ℃　时间：2020-03-22 09:39:23

解答

A
句中有具体时间就是过去时,而表示已经发生的又不指出明确时间就是现在完成时