Answer:
The best answer would be the third sentence: "The new school directory is out, it contains the names and phone numbers of all the students in the school".
Step-by-step explanation:
The third sentence is the best answer because it is correctly punctuated, there is only one comma after the first statement separating the rest of it, which is an explanation of the first. The first sentence is totally wrong because the semicolon and colon are misplaced in it and there is no necessity for using them where they are. The second sentence is also misplacing the colon, which is more common for separating headings and subheadings, and that is not the case for this sentence. The fourth sentence is also misplacing the semicolon, which fragments the sentence when and where it is not needed.