单项选择题
Stuffer-braid rope has（）.
A.a yarn core B.no core C.three strands D.12 threads
单项选择题 Serving is（）.
单项选择题 Separating both blocks of a tackle to prepare it for reuse is called（）.
单项选择题 opes or wires attached to derricks to prevent them from swinging during cargo handling operations are（）.
