26个字母中能够单独构成单词的两个字母是 .

This important lesson by Professor Wang teaches primary students how to ________ themselvesfrom danger.[ ]

Are you satisfied with what he did？　　—No， it couldn’t have been ______.

Be quiet! I have ______ to tell you.

_______ number of people poured into the cinema, and I lost ___________ sight of Alice in the crowd.