Principal White has been working in the school for about 20 years,      all his energy to teaching and

researching as well as the running of a healthy school.   [ ]

A. devoted

B. devoting

C. to devote

D. and devote

影响行业的外部因素不包括( )。

A．国民经济

B．外部经济

C．国家政策

D．企业自身规模效益