Science is my most difficult subject I will have to spend a little more time studying my classwork in order to do well in it. where do i add commas or semi colons

Choose the sentence that is not logically connected in the paragraph. (1) one final effect of radio and tv on the language must must be noted. (2) there is no doubt that these great media of information have cut down considerably the time that used to be devoted to reading. (3) radio and tv may enhance the spoken word. (4) they tend to lower comprehension levels.