Final answer:
The correct answer is Option A. The system of equations y = x and y = -1 has exactly one solution, which is x = -1 and y = -1.
Step-by-step explanation:
If we are given the system of equations y = x and y = -1, we can determine the number of real solutions without graphing or performing any substitutions. Since the second equation directly specifies that y must be -1, any solution must satisfy this condition. Substituting y with -1 in the first equation, we get -1 = x. This means there is exactly one solution to this system: x = -1 and y = -1. Therefore, the correct answer is OA.