Explanation:

Correct answer is (a). The term ‘knee-perk reaction ‘ is illogical.
‘Knee-jerk reaction’ is a phrase that means a prompt action or an action without a thought process.
‘Knee-crack reaction’ is illogical.
‘Knee-deep reaction’ is a phrase which means deeply involved.
‘Knee-drop reaction’ is a wrestling attack.
Correct sentence- Some respondents do agree these are knee-jerk reactions and a more scientific approach was needed to tackle pollution. Hence option A is correct.