Noun + Preposition / Adjective + Prep

[Emanuelli]

It was very kind of all of you to answer the questions I sent last night. I have a question: Is everybody who answers the questions, teachers??? (please, let me know if my structure in the question was correct.)

1. With the adjective "happy", I can use the prepositions: with, about, that, at depending on the sentence. Is it right?

2. Is the expression: "on account of" formal or informal???

3. In the sentence: "The first thing she has to do is listen to any new CDs." Why didn't the writer use "to" or "ing" before the verb "listen"? I mean, I have "verb to be" before it, so I guess I'd say: "The first thing she has to do is to listen/listening to any new CDs. Would it be possible? Why (not)???

Thank you very much.

[Alc112]

3. In the sentence: "The first thing she has to do is listen to any new CDs." Why didn't the writer use "to" or "ing" with the verb "listen". Would it be possible? Why (not)???

Thank you very much.

He/she used to because the verb needs that preposition, but What are you listening to?