As for how to promote public education, Professor Li gave us a lot of suggestions which _____ reasonable and practical. 

A．appeared

B．sounded

C．looked

D．listened

吹气式压力计，如果节流元件的（）足够大，只要节流元件前的压力p1变化不大，并满足节流元件后的压力p2小于或等于（）p1时，就可以达到气源流量恒定的要求。