This is an exercise that will help you learn the differences between frequently confused words. We call them "Appropriate Words" sentence completion exercises because the key thing to learn here is the appropriate context in which you should use these words. Sometimes you can use both words, but one answer is more appropriate to use in that context. For other sentences, one word is the only possible answer. The explanations at the bottom of each page will clarify all of the answers if you're not sure about certain sentences.
***You can find an explanation of the answers for this exercise in this blog post about frequently confused words.***