Error spotting (exam direction): Choose the erroneous part — mark D if there is no error — 'I am thinking of / to go to Agra / for my cousin's marriage. / No error.'

Given sentence parts (A–D)
A. I am thinking ofB. to go to AgraC. for my cousin's marriage.D. No error.

Concept/Approach (verb + preposition + gerund)
After the preposition of, use a gerund (-ing form), not an infinitive.

Step-by-step correction
1) 'thinking of to go' → 'thinking of going'.2) Correct sentence: 'I am thinking of going to Agra for my cousin's marriage.'

Common pitfalls
Using 'to + verb' after prepositions (of, in, on, about, for, etc.).

Final Answer
B — use the gerund: 'thinking of going …'