施工项目的建筑面积为( )时，需要设置3名安全管理人员。

A．1万m²及以下
B．1万～3万m²
C．3万～5万m²
D．5万m²以上

—Could you please do some shopping for me, Mary?

—Sorry, I ______ my homework. [ ]

A. do

B. am doing

C. have done

D. was doing