Which of the following subsets of C^3 (complex) are subspaces:

a) {(a,b,c) in C^3 | c=0}

b) {(a,b,c) in C^3 | |a| is less than or equal to |b|}

c) {(a,b,c) in C^3 | |a^2| + |b^2| + |c^2| =0}

I'm having trouble understanding how to use vector addiction and scalar multiplication to see if they are subspaces or not. Any help is appreciated.