One of the things that made me long ________ back in prison was that I had little opportunity thinking and reflection.

A．be

B．being

C．to be

D．to being

已知反应：H₂S(g)＋aO₂(g)=X＋cH₂O(l)　ΔH，若ΔH表示该反应的标准燃烧热，则X为  (　　)

A．S(s)

B．SO₂(g)

C．SO₃(g)

D．SO₃(l)