Answer:
Those are all correct except number 3, trust me, I don't know why they marked the rest wrong.
The past perfect would be "había enviado"
Answer:
to purchase to sell to shop to spend
The answer is estudiamos.
Remember that the subject is nosotros (we) and we would have to match the subject and the verb by conjugating the verb. A nosotros conjugation is always 'amos' in an ar verb.
I'm not going to answer this because I don't know what it is asking, but I will translate each word.
escuchario = hear it
decÃrmelo = tell me
Salir = go out
servÃrnoslo = serve us
barrerla = sweep the
hacerlo = do what
Hope I helped!