( )不属于目标型调查法．
A．选择法
B．序数表示法
C．正误法
D．描述调查
参考答案：D
It is an interesting story and one can't put it down _____ one has finished reading it.[ ]
A. after
B. when
C. since
D. until
扭曲环装入气缸中为什么会产生扭曲的效果？它有何优点？装配时应注意什么？
