( )仅适用于定心精度要求不高、载荷平稳和低速的连接。
A．平键B．楔键C．半圆键D．花键
参考答案：B
Great changes ____in my hometown in the past few years. [ ]
A. were taken place
B. have been taken place
C. took place
D. have taken place
为了直观反映两种眼部疾病的患病率随时间推移的变化速度，应选择（）
A.普通线图
B.半对数线图
C.多边图或直方图
D.散布图
E.抛物线图
