Find the incorrect part of the sentence:
I have visited Agra last month.

Correct option is A

Option (a) contains an error.
Detailed explanation of error: “Last month” is a finished/definite past time marker, so the sentence must use Simple Past (“visited”), not Present Perfect (“have visited”). Present Perfect is not used with explicit past-time adverbs like yesterday, last week/month/year, in 2010, etc.
Grammatical rule used: Use Simple Past for completed actions at a definite past time. Use Present Perfect for life experience/recent past with no definite time, or with since/for/already/just/yet/recently/so far.
Example:
✗ I have visited Agra last month. → ✓ I visited Agra last month.
✓ I have visited Agra several times. (no definite time mentioned)
Information booster: Present Perfect commonly appears with since/for/ever/never/just/already/yet/recently/so far; avoid it with yesterday/last…/ago/in + past year/date.