沉桩宜采用（）
A.重锤重击，高提捶打
B.轻锤重击，高提捶打
C.重锤低击，低提捶打
D.轻锤低击，低提捶打
参考答案：C
What is the disadvantage for air transportation?（）
A.Quick but not safe
B.Less frequency
C.It can’t lift heavy goods
D.The highest cost in all transport modes
