Peter was so excited _________ he received an invitation from his friend to visit Foshan.

A．where

B．that

C．why

D．when

《煤矿矿井机电设备完好标准》中规定，螺栓不得弯曲。螺栓螺纹在连接件光孔内部份不少于（）螺距。沉头螺栓拧紧后，沉头部不得高出连接件的表面。

A.1个

B.2个

C.3个

D.4个