下列不属于机械方法防松的装置是（）。
A.止动垫圈防松
B.双螺母止动放松
C.串联钢丝防松
D.开口销与带槽螺母防松
参考答案：B
— Did you have anyone _____ the trees?
— Yes, I had the trees _____. [ ]
A. to water; water
B. to be watered; watered
C. water; to be watered
D. water; watered
花束制作除了采用螺旋式固定花枝外，也可采用（）式固定。
