This would be false because it will depend on the actual values of both a and b, including if they are positive or negative.
This is true.
For example :
B = -6
A = -9
A + B = C = -6 + -9 = -15.
The value is C has the same sign as B.
B = 2
A = -5
A + B = -5 + 2 = -3.
Here The sign for C does not match the sign for B, which is positive.