The answer is “is”.
Since the sentence begins with “it is important”, “is” is a present tense word. This means that any past tense words are wrong, so we can cross of “was”. Now with the next answer down, “be”, it just sounds wrong. “It is important that each patient be comfortable.” doesn’t flow well, so we can cross that off too. If it was rephrased as “It is important for each patient to be comfortable”, then it might work but it isn’t. The best answer would be “is”, because it is present tense and sounds right.