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题目内容
（国家开放大学理工英语1）
Now this tiny housing solution is ______________ in urban areas in the U.S., and Canada.
选择一项：
A.
gain ground
B.
gain ground on
C.
gain ground upon
选择一项：
A.
gain ground
B.
gain ground on
C.
gain ground upon
参考答案
