烧伤瘢痕晚期整形手术，气管插管困难者处理应为（）。 A.选用放置喉罩 B.选用纤维喉

物质由分子、       、       等微利构成。如：二氧化硫是由     　（填微粒名称、下同）构成；氯化钠是由      和        构成。

If it is __________ for you to go out tonight, would you like to go to the cinema with me?

A．practical

B．necessary

C．convenient

D．grateful

You should keep _____ while I take a photo of you. [ ]

A. calm

B. quiet

C. still

D. silent

还盘一经作出，原发盘即告失效。( )

什么是种子的发芽率？