Answer:
... John and Mary are equal.
Step-by-step explanation:
We can use basic logic reasoning to complete this sentence. We have two premises that, being true, lead to a conclusion.
Premise 1: All citizens are equal.
Premise 2: John and Mary are citizens.
In that case, John and Mary are equal. They are citizens, and all citizens are equal. At no point, we are told John and Mary are an exception to this fact. So, John and Mary's being equal is the only logical conclusion from the two premises we have.