"I'm more nervous right now than when I ______," Jane said, as she saw the group of reporters waiting anxiously at the exit of the gym.

A．had competed

B．compete

C．was competing

D．have competed

对于一个静定桁架结构，如果其中一根杆元件的横截面面积增大一倍，其它条件不变，则这根杆元件的内力（）。

A.增大

B.不变

C.减小

D.无法确定，不同的结构有不同的结果