Sentence:  4 Is it necessary to <WSD>revise</WSD> vocabulary (= study it again for a second or third time)? / 5 Is it better to <WSD>revise</WSD> vocabulary occasionally for long periods of time, or is it better to <WSD>revise</WSD> regularly for short periods of time? 
Meaning of the word marked with <WSD> tags:  To look over again (something previously written or learned), especially in preparation for an examination.