The bad weather made difficult for the birds .
A. it; migrate
B. that; migrate
C. that; immigrate
D. it; to migrate
网友回答
A. it; migrate
B. that; migrate
C. that; immigrate
(答案→)D. it; to migrate
解析：考查代词。句中it作形式宾语，真正的宾语为不定式to migrate。句意：坏天气使得迁徙的鸟儿变得很难。