Answer:
A
Anthony has been practicing yoga by himself for three years and can easily fold up like a pretzel.
Step-by-step explanation:
Option A is the option that uses an intensive pronoun to complete the sentence.
Intensive pronoun refers to the pronoun that are usually used to add emphasis. These pronouns add the emphasis to the subject or add the emphasis to the antecedent of the sentence. It is similar to reflexive pronouns but they differ in function. They usually end with "self" or "selves". Examples are yourself, herself, myself, himself, ourselves, etc.
From Option A, we will discover the use of himself; which is the intensive pronoun.