Recent Research Has Found the Following with Regard to the Causes

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

A) Food colours 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