Which sentence is correct when using the verb 'recommend'?

The sentence "I recommended he rest for 5 days" demonstrates the correct usage of the verb "recommend." In English, when using "recommend," it is common to follow it with a clause that conveys what is being recommended, typically structured with the subject and the base form of the verb, as seen with "he rest." This grammatical structure effectively communicates a suggestion or advice about the necessary action.

The structure aligns with the intention behind the verb "recommend," which is to express a positive endorsement or suggestion toward a specific course of action. In this case, it tells the reader that it is advisable for the individual to take a rest.

Other options either misapply the verb "recommend" or use less appropriate grammatical constructions. For example, "I recommend to rest for 5 days" incorrectly uses the infinitive "to rest" after "recommend," while "I suggested to rest for 5 days" does the same with "suggested." Additionally, "I advised rest for 5 days" lacks the clarity of subject-action that a clause provides. Therefore, option C not only follows grammatical rules but also clearly conveys the intended meaning.