Hello people!

I have an english test tomorrow and I need help. That test/exam will test our knowledge in the Passive Voice, but there are some things that aren't clear to me.
Here are some exercises that are going to be on test:
1. Change the sentences into the present passive:
a) Lots of children watch TV.
b) My brother is cooking dinner.
c) We eat too many sweets.
My answers:
a) TV is watched by lots of children.
b) Dinner is cooked by my brother. (is or was??)
c) Too many sweets are eaten by us. - (Hmm? Is it right? It doesn't make sense for me.)
2. Write the questions in the passive:
a) Who/television/invent/by?
b) When/Gandhi/kill?
c) Where/first plane/fly?
My answers:
a) Who invented television by?
b) When was Gandhi killed? (Or... ? I don't know! It really makes me angry!

)
c) Where did first plane fly? (I know it isn't right, but I don't have any idea how to do it)
That's what I want to know. Will someone find some time to take a look at this and tell me what's wrong and what's right?
Thanks in advance.
