She (look) very worried for the past few days.

Correct option is C

• A) Have looked: This form is incorrect because it uses the present perfect tense, which doesn't match the context of something occurring over a specific period in the past.

• B) Looked: This past tense form is too simple and doesn't convey the continuous nature of the state over the past few days.

• C) Had been looking: This past perfect continuous tense is correct because it indicates an action (or state) that was ongoing in the past and completed before now.

• D) is looking: This present continuous tense is incorrect because it suggests the action is happening at this very moment, not over the past few days.