Final answer:
Option C, 'because he got new paints,' is the correct dependent clause to complete the sentence as it starts with a subordinating conjunction 'because' and cannot stand alone.
Step-by-step explanation:
To identify a dependent clause that can be added to the sentence 'Nick went to the painting class _______________,' one must look for a group of words that cannot stand alone as a sentence and starts with a subordinating conjunction. The options provided are A. for three weeks B. after school C. because he got new paints D. and tried his new paints. The correct answer is C. because he got new paints. This clause is dependent because it begins with 'because' which is a subordinating conjunction, meaning it relies on the main clause to complete its meaning.