Parts of the following sentence are given as options. Identify the segment that contains a grammatical error.
Avoid the crowd becomes impossible while travelling in a metro.

Correct option is B

Option (b) contains an error.
Detailed explanation of error: The subject of the sentence is a verbal idea and must be expressed with a gerund (-ing form) or a to-infinitive when functioning as a noun. “Avoid the crowd” is a bare verb phrase; it should be “Avoiding the crowd” (gerund as subject) or “To avoid the crowd”. The rest of the sentence is acceptable.
Corrected sentence: Avoiding the crowd becomes impossible while travelling in a metro.
Grammatical rule used:
· When a verb functions as the subject of a sentence, use a gerund (V+ing) or to-infinitive: Swimming is fun. / To swim is fun.
· A bare infinitive or base form cannot act as the subject in standard usage.
Example: Finding a seat becomes difficult during rush hours.
Information booster / exceptions:
· After certain verbs and prepositions, only a gerund is used: He insisted on going. ( on + V-ing).
· With expressions like “It is no use/no good/It’s worth”, we use a gerund: It’s no use arguing.