Answer:
Option 1. (for three weeks)
Step-by-step explanation:
Correct Answer:
"Nick went to the painting class for three weeks"
This has a subject (Nick), Verb (went), and the idea behind it is that he "went to the painting class for three weeks."
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"Nick went to the painting class after school."
This one could also work. Although I am positive it is incorrect.
"Nick went to the painting class and he tried his new paints."
There is no proper grammar.
"Nick went to the painting class because he got new paints."
Again, there is no proper grammar
Conclusion: Option 1 (for three weeks.