Every device ______in the plane must be designed and made with great care so as to make sure that nothing goes wrong in operation.

A．fitted

B．to be fitted

C．fitting

D．being fitted

产生谨慎动机的原因是（）。

A．分散风险

B．抓住有利投资机会

C．未来收入和支出的不确定性

D．收入和支出在时间上不同步