Some buildings built in the past _______ down and new ones are being built there.

A．will be pulled

B．had been pulled

C．have been pulled

D．are pulling

线脚的工艺制作设计，是根据线脚构造设计的要求，定出杆件的( )，制定线脚制作的各道工序和相应的工作内容。

A．材料

B．基本形状

C．宽度

D．厚度