A _______ dog seldom bites.

সঠিক উত্তর হবে: Barking.
This is an example of present participle.

Participle:
- It is the form of a verb that usually ends in "ed" or "ing" and is used as an adjective:
- Participle একই সাথে Verb ও Adjective এর কাজ করে।

In the sentences "He's sleeping" and "I've already eaten", the words "sleeping" and "eaten" are both participles.

Participle মূলত: তিন প্রকার:
1. Present Participle. Ex: Do not disturb a sleeping dog.
2. Past Participle. Ex: This is a book written by Charles Dickens.
3. Perfect Participle. Ex: Having eaten rice, he went to bed.

Use of Participle:
1. To form a verb: They are playing football.
2. As Adjective: The book is interesting.
3. As Absolute: We will go there, God willing.

Source: BBC learning english website
A passage to the English Language by S.M. Zakir Hussain.