The food safety is a serious _______ in our country. We should try to solve it.
A：subject
B：program
C：problem
D：opinion
①给试管加热；②熄灭酒精灯；③检查气密性；④把高锰酸钾装入试管，在试管口堵一小团棉花，用带导管的胶塞塞紧，固定在铁架台上；⑤用排水法收集氧气⑥从水中取出导管。（ ）
若p是真命题，q是假命题，则（ ）
I like to go to school _______ foot on sunny days but go _______ bus on rainy days.
尊重朋友，首先要懂得 （ ）
