A:reliable
B:determined
C:stubborn
D:tired
——Does he often _________?
——No, he often goes to bed early.
将一个充满CO2的试管倒插在澄清石灰水的烧杯里,可观察到的现象是:____;____.
对刚出生的婴儿接种卡介苗,可以预防结核病,接种的目的主要是( )