help needed in Engilsh for BITSAT

P.S. I don't have the answers. In these qsn i am having a doubt..please help...

1)How long ____________________??

a) you are waiting b)are you waiting c)you have been waiting d)have you been waiting

my doubt B and D...why/why not

2)I gave him _____________ he wanted.

a) which b) what c)that d)that which

my doubt B/D.why/why not..

3)Open the book _____page 45.

a)in b)at c)on d)for

4)The pickpocket got ________________ only with a warning.

a)off b)along c)over d)through

again my doubt B/D.why/why not..

5)The room________________yesterday.

a)cleaned b)has cleaned c)was cleaned d)has been cleaned

my doubt C/D.why/why not...

will keep adding more....