问题描述：
______has been done to improve the working conditions A,a lot of B,lots of C,many D,much
______has been done to improve the working conditions
A,a lot of
B,lots of
C,many
D,much
请帮我分析下为什么
______has been done to improve the working conditions
A,a lot of
B,lots of
C,many
D,much
请帮我分析下为什么
问题解答：
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