How to get a subscript of a vector?

Hi,
?which()
?which(A==2)
#[1]? 3? 7 10
A.K.

Suppose there is a vector 
A <- c(1,3,2,6,7,8,2,1,3,2). 

Now, I want to get the subscript of elements of A which equal 2. 

How can I do it ?