In both 2004 and 2009, which drug contributed to the most emergency room visits by people under 21?

21.2 percent involved illicit drugs  14.3 percent involved alcohol, in  combination with other drugs.

(either alone or in  combination with another drug) increased  98.4 percent between 2004 and 2009,  Patients aged  20 or younger accounted for 19.1 percent  (877,802 visits) of all drug-related visits in  2009; about half of these visits involved  drug abuse.

i think your answer is a. coordination