卷扬式启闭机的优点不包括（）。
A、可以获得较大的启门力
B、行程实际上不受限制
C、具有较大的灵活性
D、卷扬式启闭机有自锁作用
参考答案：D
I will never forget the day _____ Shenzhou VII was launched, _____ has a great effect on my life.
[ ]
A. when, which
B. that, which
C. which, that
D. when, that
切缝机导向不规则摆动的原因及处理方法有哪些？
