They stoppedquarrelingas soon as their father arrived. The underlined part here is an example of -

• They stopped quarreling as soon as their father arrived. The underlined part here is an example of - Gerund.

• Gerund: 
- Verb এর সাথে -ing যোগ হয়ে যদি noun এর কাজ করে, তাকে Gerund বলে।  
- Gerunds don’t describe the action, they act as nouns. 
- The Gerund has the force of a noun and a verb; it is a Verbal noun. 
- এখানে  ‘quarreling’ transitive verb stopped এর object হিসেবে বসেছে।
- তাই এটি gerund.

• Functions of the Gerund: 
কোন বাক্যে Gerund ব্যবহৃত হয়: 
1. As subject: Rising early is a good habit. 
2. As object: I like playing Badminton.
3. As an object of a preposition: The old woman is tired of walking.
4. As a complement of a verb: Working is earning.