什么叫助燃物?
参考答案:
与可燃物质相结合能导致燃烧的物质。
I used to feel very nervous when I stood up in front of others, but now I feel quite ______when giving a speech to the school.
A.at random
B.at length
C.at ease
D.at sight
热水供应管道应采用耐压管材及管件,通常可以采用( )。
A.聚氯乙烯管
B.铝塑管
C.交联聚乙烯管
D.聚乙烯管