He is very experienced ______ looking after animals.

The correct answer is - ক) at
Full Sentence is - He is very experienced at looking after animals.

• Experienced at
- কোনো কাজে দক্ষ বা অভিজ্ঞ বোঝাতে ব্যবহৃত হয়।
- Be experienced at + Verb-ing
- Example: He is very experienced at looking after animals.

• Experienced in
- কোনো ক্ষেত্র বা বিষয়ের ক্ষেত্রে অভিজ্ঞ।
- Be experienced in + Noun
- He is experienced in management.

Source: Cambridge Dictionary.