单项选择题

This line was carrying equal number of eastbound and westbound trains, and they ______ regularly.

A．altered
B．alternated
C．switched
D．exchanged
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单项选择题
During the famine of 1943, millions of peasants ______ to the cities because they could not make a living in the countryside.
A．immigrated
B．emigrated
C．migrated
D．generated
单项选择题
What the government should do urgently is to take actions to ______ the economy.
A．brook
B．blush
C．boost
D．brood
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