将下列工业基地的特点选出来

______京津唐地区         A 以重工业为主的工业基地

______沪宁杭地区         B 北方最大的综合性工业基地

______珠三角地区         C 全国最大的综合性工业基地

______辽中南地区         D 以轻工业为主的工业基地．

His mother looked very tired，for she _____ the house herself all day.

A．had cleaned

B．has been cleaning

C．had been cleaning

D．has cleaned