Identify the option that most appropriately combines both the given sentences into one sentence.
He was adamant about refusing the honour bestowed upon him. He did not trust the credentials of the organisation that intended to recognise his contribution.

Correct option is C

The correct option is (c) because the word "since" is used to establish a cause-and-effect relationship between his refusal and his mistrust. The sentence now reads smoothly, showing that his lack of trust in the organisation’s credentials is the reason for his refusal.
Option (a) is grammatically incorrect due to the redundant use of "as because," option (b) uses "due to" incorrectly, and option (d) introduces an inappropriate condition ("whenever") that does not fit the context.