I saw him (go) there.

Explanation: সঠিক উত্তর হবে: going
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। 

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: A passage to the English Language by S.M. Zakir Hussain.