Recent Research Has Found the Following with Regard to Causes

Recent research has found the following with regard to causes of ADHD:

A) Food colors and additives, which for years were thought to cause ADHD, then later refuted, now appear to have a small but measurable impact on increased levels of hyperactivity.
B) Pesticides found in foods may be a contributing factor to an increased risk of ADHD.
C) Both a and b
D) Neither a or b