所有的变形位置（）正确的矫正位置。
A.都是
B.都不是
C.不一定是
D.一定是
参考答案：C
The service life of distress signals must be not more than（）.
A.forty two months from the date of manufacture
B.thirty six months from the date of the last inspection
C.twenty four months from the date of approval
D.twelve months from the date of purchase
泥灰岩
