-----where has his brother been ?

------No one knows. He has returned home safely but his missing made the police _____ .

A．to puzzle

B．puzzling

C．puzzled

D．be puzzled

为了防止多次使用内螺纹芯头导致齿顶角超标的现象，在起始拉伸时一般将齿顶角调整在（）较合适。

A.技术要求齿顶角最小值

B.技术要求齿顶角最大值

C.超出技术要求齿顶角最小值

D.超出技术要求齿顶角最大值