Direction: Find the correct sentence from the given options.

Concept: A reflexive pronoun (myself, yourself, himself, herself, itself, ourselves, yourselves, themselves) must agree with its antecedent — a subject already stated in the sentence, or implied as in an imperative ("Help yourself") — in person, gender, and number; it can never itself function as a sentence's subject, or as part of a compound subject. It is used either as an intensifier right after the noun/pronoun it emphasizes (e.g., "I myself opened the store") or as the object of a verb whose action reflects back on the subject (e.g., "He hurt himself"). With a separable verb-particle pair such as "keep away," the reflexive object is inserted between the verb and the particle ("keep yourself away"), not tacked on after the whole phrase.

Application: In "She herself completed the whole work," the reflexive pronoun "herself" sits immediately after the subject "She" as an intensifier, agreeing with "She" in person (third), gender (feminine), and number (singular) — exactly the intensive-reflexive pattern the concept describes, so the sentence is grammatically correct.

Cross-check: Testing the other three constructions against the same agreement-and-usage rule shows exactly where each breaks down:

• "He themselves took the responsibility" pairs the singular subject "He" with the plural reflexive "themselves" — an agreement mismatch.

• "You should keep away yourself from pollution" places the reflexive pronoun after the full phrasal verb "keep away" instead of between the verb and its particle; the grammatical word order is "keep yourself away from pollution."

• "You and himself were best friends in the college" uses "himself" as part of the sentence's subject; a reflexive pronoun cannot function as a subject on its own — a personal pronoun such as "he" is needed there instead.