Correct Answer: (c) He was adamant about refusing the honour bestowed upon him since he did not trust the credentials of the organisation that intended to recognise his contribution.
Solution:The correct answer is (c) because it combines the two sentences appropriately and grammatically 'He was adamant about refusing the honour bestowed upon him since he did not trust the credentials of the organisation that intended to recognise his contribution.' The word 'since' correctly indicates the reason for his refusal.