"Running is a good exercise to stay fit"; this was her realization after participating in the race." How many nonfinite verbs are present in the sentence?

- The correct answer is 3.  এই বাক্যে মোট তিনটি  nonfinite verb আছে। 
- ১ টি করে, Participle, gerund and infinitive আছে। যেমন:
1. running= gerund
2. to stay= infinitive 
3. Participating= Participle

A finite verb is a 'working' verb with a subject; it can be any tense. 
A non-finite verb which is also called in infinitive verb has no subject and can't be in all the tenses.

A non-finite verb can be:
i) an infinitive
Example: walk/to walk; be/to be; be interested/to be arrested

ii) a present participle
walking; being; being interesting

iii) a past participle
walked; been; interested

A sentence must have at least one subject and finite verb.

Source: Cliff's TOEFL, Oxford Practice Grammar by J.Eastwood