What must be true of two rational expressions before they can be added?
They must have common numerators.
They must be of the same degree.
MIM They must have the same variables,
The must have common denominators.

They most have common denominators.

Step-by-step explanation:

Let the following two rational expressions:

where p,a,q, b are integers, a and b the denominators are not 0, i.e.

We can add rational expressions only if their denominator is same.

That is why we find LCD to be .

Then,

Let the following two rational expressions:

where p,a,q, b are integers, a and b the denominators are not 0, i.e.

We can add rational expressions only if their denominator is same.

That is why we find LCD to be .

Then,

So, the correct answer is the last option that we can sum rational expressions if they have common denominator.

step-by-step explanation: