Which one of the following identities is the result of comparing the coefficients of x^r in(1+x)^n+2=(1+x)^2?
A.C(n+1,r)=C(n,r)+C(n,r-1)
B.C(n,r)=C(n-1,r)+C(n-1,r-1)
C.C(n+2,r)=C(n,r)+C(n,r-1)+C(n,r-2)
D.C(n+2,r)=C(n,r)+2C(n,r-1)+C(n,r-2)
