Mark was a student at this university from 1999 to  2003,______he studied very hard and was made    

Chairman of the Students' Union.     [ ]

A. during which time        

B. for which time    

C. during whose time        

D. by that time

现代企业制度的组织形式主要有______。

A．有限责任公司

B．合作制

C．合伙制

D．租赁制

E．股份有限公司