The words that complete the sentence correctly are the following ones: "allow" and "aloud". Therefore, the sentence would be as follows: Elementary school students are not allowed to talk while the teacher reads aloud after lunch.
These words (allow and aloud) are homophones. They are words that have the same pronounciation but are different in meaning, origin and spelling. Allow has to do with permission, that is, it means to let someone have or do something. On the contrary, aloud means audibly, not silently.
