题目内容
-There ______ many trees at the foot of the mountain.
--But now they are slowly disappearing because of human activities.
A.is used to
B.used to
C.used to be
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题目内容
-There ______ many trees at the foot of the mountain.
--But now they are slowly disappearing because of human activities.
A.is used to
B.used to
C.used to be