Here's a swap and check exercise to consolidate modal verbs for expressing degrees of certainty in the past. There are a and b versions of worksheets on the same topic. You can divide your class into two and give them separately. Then, your students should swap them to check each others' worksheets. It'll be great for increasing classroom interaction and your students will love checking their friends' worksheets. Before giving out these worksheets, you can review this subject with this worksheet. An answer key is also included.