Answer:
has to take the medicine
Step-by-step explanation:
A verb is used to express an occurrence, action, or state. It is the grammatical centre of the predicate in a sentence.
An auxiliary verb is a verb which is used in the formation of tenses, moods, tones, etc. Has to is correct as three times a day indicates the use of has to (to suggest compulsion and necessity)
The other option are wrong as no other tense can be used here.