钴铬合金全冠抛光所用抛光剂是

A．氧化铁

B．氧化铬

C．硼砂

D．浮石

E．石膏

In the context of company law, explain the meaning of the following duties owed by directors to their companies:

(b) the duty to exercise reasonable skill, care and diligence; (4 marks)