Ok the question says complete the group table to G = {a,b,c,d}

We are given this

x a b c d

a

b a

c a

d

I know that each element can occur only once per row/column and that one element needs to be the identity i just cant figure out which one im pretty sure if you figure out what element is the identity it wouldnt be to hard to fill in the rest im just unsure about how to figure it out.