Answer:
The answer is letter C) to avoid harmful exposure to the sun's direct rays.
Step-by-step explanation:
An infinitive phrase begins with an infinitive - to + verb - and can function as a noun, an adjective, or an adverb. A complete infinitive phrase includes everything that is a part of it: the infinitive, the objects, the modifiers.
In the sentence "It is important to avoid harmful exposure to the sun’s direct rays," the infinitive phrase begins at "to avoid". Everything that comes after "to avoid" is part of the phrase. Thus, the best option is letter C) to avoid harmful exposure to the sun's direct rays.