What must be true of two rational expressions before they can be added? a they must have common numerators. b they must be of the same degree. c they must have the same variables. d the must have common denominators.

D They must have common denominators.

Step-by-step explanation:

Rational expressions are fractions formed by two polynomials, one in the numerator and other in the denominator.

The numerator is the polynomial that is at the top of the fraction and denominator is the polynomial that is at the bottom of the fraction.

To add any fractions it is necessary that they have the same denominator, this applies to rational expressions, to add them it is required that they have the same polynomial in the denominator.

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step-by-step explanation:

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step-by-step explanation: