I am bit confused of the singular or plural choice when it comes to the belonging relation of two things when using the X of A and B.
I'd like to express that A and B both own the same type of uncountable or singular countable property. A naive example wound be
The climate of country A and the climate of B is/are(?) different.
Does the contraction affect the choice?
The climate of country A and B is/are(?) different.
How about the property is countable but A and B each has only one.
The president/presidents(?) of country A and B is/are(?) different.