Q1. Choose the option that correctly fills in the blank. The clerk insisted ___ checking every receipt before closing the cashbook.
Explanation
The rule is that 'insist' takes the preposition 'on' before a noun or gerund. The cue is the gerund 'checking' after the blank. Therefore 'insisted on checking' is the only correct form; 'for', 'to', and 'at' do not form the required collocation with 'insist' in this sentence.
