Both a b c are the right answer choice for this question
Answer: died
Explanation: Simon was dead, and Jack had died. 'Was' is a past continuous tense word showing an action that had been performed moments, seconds, minutes or even years ago, and that action or event will continue to be in the past. 'Had' on the other hand is showing an event that just occured recently. Simon might have died 2 days ago and Jack's death might have come seconds ago.
The term used to describe an organic cofactor is that this common chemistry allow cells to use a small set of metabolic intermediates to carry chemical groups between different reactions. These group-transfer intermediates are the loosenly-bound organic cofactors, often called coenzymes.
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