A) Unlike decreased by large amounts, small amounts of alcohol increase neurogenesis. -- Modifier placement error. The entity that is decreased should come after the comma. Eliminated.
B) Small amounts of alcohol increase more neurogenesis, as compared to large amounts. -- "more" seems redundant here since "increase" is already given. Eliminated (But we will come back to this choice in case follow-on choices aren't better since redundancy isn't a hard and fast elimination rule)
C) Small amounts of alcohol increase neurogenesis, whereas large amounts decrease it. -- Seems fine. No issues. Correct choice.
D) As compared to large amounts, neurogenesis is increased by small amounts of alcohol. -- Illogical comparison. Large amounts seems to be compared with neurogenesis rather than small amounts.
E) Small amounts of alcohol increase more neurogenesis, as compared to large amounts do. -- same as B