工程建设项目招标投标活动进行投诉时，投诉人提交的投诉书应当包括( )。

A．投诉人的名称、地址及有效联系方式

B．被投诉人的名称、地址及有效联系方式

C．投诉事项的基本事实

D．投诉人上级主管部门意见

E．相关请求及主张

Class Two ____ taking their lessons when there was a knock at the door. [ ]

A. is

B. are

C. was

D. were