Select the correct active form of the given sentence.

Let the medicine be administered every four hours.

Administer the medicine every four hours.

The correct active form of the given sentence is Administer the medicine every four hours.

The sentence "Let the medicine be administered every four hours" is in the passive voice. The passive voice is formed by putting the subject of the active sentence after the verb "to be" and the past participle of the main verb. In this case, the subject of the active sentence is "the medicine" and the main verb is "administer." The past participle of "administer" is "administered." So, the passive form of the sentence is "Let the medicine be administered every four hours."

The active voice is formed by putting the subject of the passive sentence before the verb and the past participle of the main verb. In this case, the subject of the passive sentence is "you" and the main verb is "administer." The past participle of "administer" is "administered." So, the active form of the sentence is Administer the medicine every four hours.

The other options are incorrect because:

• You have administered the medicine every four hours is in the past tense, while the original sentence is in the present tense.
• Let you administer the medicine every four hours is grammatically incorrect. The verb "to let" is followed by a noun or pronoun, but the phrase "let you administer" is not a noun or pronoun.
• You are administering the medicine every four hours is in the present progressive tense, while the original sentence is in the simple present tense.