Question: What is virus attenuation in practical terms for successful vaccine discovery?
A: Passage of live virus from cell to cell and a search for less virulent mutants
B: As (a) but using low temperature (33oC) to select cold adapted mutants
C: Direct random mutagenesis to create a less virulent mutant
D: Recovery of a naturally occurring 'wild' virus which is naturally less virulent
Please eliminate two incorrect options first, then think it step by step and choose the most proper one option. Provide two versions of response separated with exactly 6 asterisk symbols: ******.
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