A={x|x^2-3x+2=0}={x|(x-1)(x-2)=0}={1,2}
B={x|x^2-(m+1)x+m=0}={x|(x-m)(x-1)=0}={1,m}
B为A的子集,所以有m=1或m=2.
故C={1,2}