在治理水土流失中，实施（），充分发挥大自然的自我修复能力。
A、退耕还林
B、封山育林
C、退牧还草
D、修堤筑坝
参考答案：A, B, C
行为的模式
The house was very quiet, () as it was on the side of a mountain.
A. isolated
B. being isolated
C. isolating
D. having been isolated
