Adequate intake of which nutrient has been shown to reduce the risk of neural tube birth defects?

The choices are:
A. folic acid   
B. mercury
C. vitamin D
D. vitamin C

The answer is A. folic acid
Source:https://www.health.ny.gov/publications/1335/

Based on a study, folic acid can prevent brain damages and spinal problems 70%. Giving sufficient folic acid during the first month of pregnancy can help five better health condition and prevent birt defects. There are plenty of foods containing folic acid, mainly coming from cereals, grains, and vegetables.

Try and make the question more clear : )

The answer to that question is a