China ______ a lot of people moving to urban areas in the last 20 years. However, many migrants  left their families behind.
#100122
A
saw
B
sees
C
has seen
D
had seen
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He ___articles for our wall-newspaper these three years, and he ___about forty articles. 
#104632
A
has been writing; has written
B
has been writing; wrote
C
is writing; has been writing
D
has written; has written
We were listening closely to the lecture yesterday evening when suddenly the light _______.
#102340
A
had been gone out
B
was going out
C
was gone out
D
went out