The first class is .
A:beginning
B:begins
C:begin
词汇运用 (a) 根据句意和汉语注释,写出单词的正确形式。(b)根据句意, 写出括号内所给单词的适当形式。
I often help mother__________ housework after school.
将25g20%氯化钾溶液稀释到50g,稀释后所得溶液中溶质的质量分数是( )