一个圆柱的高是12.56厘米，侧面展开后是一个正方形．这个圆柱的底面积是______平方厘米．

— Did you listen to the report last Friday?

— Yes, it was about the shortage of migrant workers. That was the first time I ____ about the subject. [ ]

A. heard

B. was hearing

C. would hear

D. had heard