1. To enter the race, the runners must fill out a form and pay a fee.
"To enter the race," is A: an infinitive phrase.
2. He used a dictionary to check his spelling.
"To check his spelling," is also A: an infinitive phrase.
*To identify an infinitive phrase*
Infinitive phrases contain "to," followed by a verb and other objects or modifiers.
An infinitive by itself is just "to," followed by a verb.
4. Somebody from the girls' volleyball team accidentally washed ____ uniform with bleach.
If we didn't know the gender of the person washing the uniform, then D: their would be the answer, as it is a gender-neutral term. But because we know the gender (somebody from the girls' volleyball team), the correct answer is C: her.