She acted as though she (knows/knew) the outcome of the experiment.

The correct option is "knew" because the phrase "as though" (meaning "as if") is used to describe an unreal or hypothetical situation. When the main clause verb ("acted") is in the past tense, the verb in the "as though" clause typically uses the past subjunctive to express a present or past unreality.

Here's a breakdown:

    
• "As though" or "as if" introduces a clause that expresses an imagined or untrue condition.
    
• When the main verb is in the past tense (e.g., "acted"), the verb in the "as though" clause should also be in a past form to maintain the sequence of tenses and indicate the hypothetical nature.
    
• "Knew" is the simple past form, which functions as the past subjunctive in this context, indicating that her knowledge of the outcome was a hypothetical or unreal situation at the time she acted. If the hypothetical action in the "as though" clause had occurred even earlier than the main verb, the past perfect subjunctive ("had known") would be used.

For example:

    
• She acts as though she knows the answer. (Main verb present, hypothetical present)
    
• She acted as though she knew the answer. (Main verb past, hypothetical past/present unreality)
    
• He talked as if he had seen a ghost. (Main verb past, hypothetical action in the past perfect)