which ????????????? to use?

[Awence]

I m boggled by this,

I have to choose which subjects i want to study, and i have chosen biology, chemistry and Maths.

May i know whether "which" can be used with plural nouns? I know in some circumstances, it is alright, like

THe stairs which i took were slippery.

Stairs here is a single entity in plural form.

But how about the first example above.

[MissLT]

Yes.

[Janette]

I think it is "Math" not "Maths."