I followed this approach:
On the basis of lab grown fullerene, the argument makes a prediction that this discovery shall help geologists in evaluationg certain hypothesis about state of Earth's crust at the time of formation of naturally occuring fullerenes.
In these types of questions, the argument uses one sample ( lab grown fullerenes) to make ageneric conclusion about the whole population (Naturall fullerenes).
Weakener: Whether these lab grown fullerenes exactly match the condition in which natural fullerenes occur? What if the conditions are different?. If this is true hat the conditions are different, then lab grown fullerenes are not representative of those fullerenes that were formed under natural conditions, hence this argument falls apart.
So answer is D