不孕症伴有痛经，常常发生于
A.多囊卵巢综合症
B.子宫内膜异位症
C.子宫内膜增殖症
D.卵巢囊肿
E.粘膜下子宫肌瘤
参考答案：B
（）的代号是P.S。
Tugs sometimes shackle a length of chain in the towline in order to（）.
A.take the wear should the towline drag bottom
B.assure that if the towline is overstressed it will part close to the bridle
C.prevent the towline from whipping should it part
D.put spring in the towline
