How to keep teens from drinking at a party where alcohol is served<br>Determine whether or not it is necessary to serve alcohol at the party. Depending on the type of party or the people there, serving alcohol may not the best choice. Try to gauge how many teens will be at the party, and the likelihood of underage drinking.
If teens drink alcohol, it is considered to be underage drinking. 
There are some regional exceptions, of course - but this context specifically talks about how to prevent teens from engaging in underage drinking, so as far as this context goes, teens drinking translates to underage drinking. My statement is paraphrased from different sentences within the context, therefore, my statement is definitely correct. This is an instance where I'm not sure how the system had difficulty, but if I had to guess, I would say that the system does not compute teens drinking and underage drinking as one and the same, which is generally untrue and definitely untrue in this specific context.
( z1 consider :ARG1 ( z2 drink :mod ( z3 underage ) ) :condition ( z4 drink :ARG0 ( z5 teen ) :ARG1 ( z6 alcohol ) ) )