Twenty students want to attend the class that aims to teach to read first.
A：what
B：who
C：how
D：why
据研究，SARS病毒有多种变异类型，艾滋病病毒HIV约有100种不同的形态，SARS和HIV能形成较多不同变异类型的根本原因是
春天，植物产生幼叶时要进行旺盛的细胞分裂，其细胞分裂方式和DNA复制的情况是（ ）
We are busy in preparing for the performance in order not to________in front of our classmates.
