This is a very easy exercise to test students´ grammar. They will have to find one error in four underlined parts of each sentence. Answers are provided with explanations of how to correct the mistakes.
I had worked as a teacher of English at a gifted high school for 7 years before becoming a full-time test developer and assessment researcher. I'm the author and co-author of nearly 50 workbooks. I'm also a member of ESLprintables as Mia2806