I see two, arguably three errors. (Scroll down.)
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The phrasal adjective crystal meth should be hyphenated since it comes before the noun it modifies—dealer.
The singular they in the phrase their teeth might be okay according to many style manuals, but I’m not a fan. I’d say his teeth. How often are these dealers women? This is your chance to educate me, O Worldly One.
Finally, it’s that old meme classic: lack of a period at the end of the sentence! Don’t let me catch you dropping your punctuation.
Trivia: Did you know that the word punctuation contains the Latin root punct-/punctus, meaning “point” or even “prick/puncture”? Think: exclamation point. The punct root is hiding in the French words, as point, for certain punctuation as well:
point d’interrogation = question mark
point d’exclamation = exclamation point
point = period
deux points = colon (lit., “two points”)
point-virgule = semicolon (lit., “period-comma”)
Punct appears in German words, too:
pünktlich = punctual
Blaupunkt (brand name) = blue point, blue dot
I could point out more examples, but I’ll stop here. You get the point.
ADDENDUM: Quizzes are now here! Visit this site, find the quiz with the relevant unit numbers, be mindful of what topics are covered in each unit, and take the quiz(zes) as many times as you want. Nothing is recorded, so don’t feel bad if you stumble. Just pick yourself up, dust yourself off, study a bit more, and try again. You can also take a “snapshot” of your completed quiz, email it to me, and I can help you review by giving you hints as to the correct answers.