This strengthens by defending the argument from the possibility that passage through cosmic dust occcurred before the ice ages starting to occur.

This helps establish that the dense cosmic dust the author’s hypothesis requires actually exists and correlates with the beginning of the ice ages.

This strengthens by showing that dust in Earth’s atmosphere can reduce Earth’s average temperature. This makes the author’s theory about dust causing ice ages more plausible. Although (C) is about volcanic dust, it still shows that dust in atmosphere can cool the Earth.

(D) tells us that cosmic rock periodically enters the atmosphere. But does the Earth get colder after this happens? We don’t know. Do these periodic entries of cosmic rock coincide with Earth’s ice ages? We don’t know. (D) has no impact.

This provides evidence of a correlation between cosmic debris and the occurrence of ice ages.