Correct the sentence with the appropriate form of the underline verb.

Parents should tell their children to exercise great care when crossed busy roads.

The correct answer is 'crossing'.

Key Points

• The correct form of the underlined verb in the sentence is 'crossing'.
• A gerund is a verb form ending in "-ing" that functions as a noun, representing an action or activity. In this case, "crossing" is a gerund that acts as the object of the preposition "when."
• Grammatically, the phrase "when crossing busy roads" serves as an adverbial clause modifying the verb "exercise." It indicates the time or circumstance when the exercise of great care is necessary—while the action of crossing busy roads is taking place.
• Therefore, using the gerund "crossing" maintains the present participle form that aligns with the ongoing action or habitual activity of crossing busy roads, making it the grammatically appropriate choice in this context.
   

Correct Sentence: Parents should tell their children to exercise great care when crossing busy roads.