冲压机的传动常用曲柄滑块机构将旋转运动变为直线运动，曲柄滑块机构运行到α=90°位置时，其速度为( )加速度为( )
A. 最大；最小
B. 最大；为零
C. 最小；最大
D. 最小；为零
在冲压设备的安全装置中，拉手式安全防护装置属于( )类型。
A. 按钮式
B. 光电式
C. 感应式
D. 机械式
Old Reese never wanted to know about his son's studies because ____________.
A. he was sure his son was good at his lessons
B. he spent all his energies on his business
C. he knew nothing about the education
D. his wife looked after their children
如果只使用1分、2分、5分、1角和5角的硬币，小马至少需要有几个硬币才能不找零地支付出任何不超过1元的钱数（）
A. 8
B. 9
C. 10
D. 11
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