树上原有36只鸟，飞走了一些，现在还剩6只，飞走了多少只鸟？
36-6=30（只）
我国西部地形多为______和______为主，东部则以______和______为主，地势特征是______．
Near here is a beautiful park ______ a big lake in it. [ ]
A. of
B. with
C. on
