Let S = R - {-1} and define a binary operation on S by a*b = a+b+ab, what is true about (S,*)
A. (S,*) is a group but is not commutative
B. (S,*) is a group and is also commutative
C. (S,*) is not a group because inverse of 1 doesn't exist
"How to check if inverse and identity element exist?