_______ puzzled Li Lei a lot was _______ his best friends didn’t come to school this morning．

A．That; why

B．That; what

C．What; whether

D．What; why

氧气的化学性质下面（）是错误的。

A.化学性质特别活泼

B.氧气能与可燃气体任意比例混合形成爆鸣气体

C.浓度越高氧化反应越强烈

D.具有强氧化性