问题
选择题
China ______ a lot of people moving to urban areas in the last 20 years. However, many migrants left their families behind.
A．saw
B．sees
C．has seen
D．had seen
答案
答案：C
题目分析：考查时态：句意：在过去的20年中中国见证了很多人搬到都市，然而，很多移民把家人留下了。时间状语是in the last 20 years表示从过去到现在一直在做的事情，用现在完成时，选C。