Speaker A: I can’t stand the school cafeteria. The food is terrible.
Speaker B: ().

A. I agree with you. It’s quite difficult to find a seat in the cafeteria.

B. Yeah, you will feel more comfortable if you sit down.

C. Yeah, but that’s not the worst thing about it. It’s also very dirty.

D. I don’t see why they don’t supply some seats for us.

过滤式自救器是通过过滤空气中的有毒有害气体，把它们转化成无毒的（），构成呼吸所需的氧供人呼吸。

A、一氧化碳

B、二氧化碳

C、氧气

D、空气