—Have you heard from Nelly recently?

— Yes, I _________ his letters and cards many times while I was in Italy.

A．have received

B．received

C．had received

D．would receive

天然气滤网液位计高高动作将导致运行中的燃气轮机（）。

A、自动降负荷

B、自动解列

C、自动停机

D、跳机