When I was younger, I ____ without stopping. (past ability)
could run
Explanation
The exercise instructs the student to complete the sentence using 'could' to express the function mentioned in the brackets, which is 'past ability'. Since 'could' is a modal auxiliary verb, it must be paired with a base verb to form a complete predicate. Adding a verb like 'run', 'walk', or 'swim' completes the sentence logically (e.g., 'When I was younger, I could run without stopping').
Solution Steps
Step 1: Identify the grammatical function required in the brackets: (past ability).
Step 2: Recall that 'could' is the modal verb used to express general past ability.
Step 3: Combine 'could' with a suitable action verb (such as 'run', 'walk', or 'cycle') to fill the blank and make the sentence meaningful.