Level G1 typically targets students aged 11–12 (late elementary to early middle school) and focuses on the following key areas:

You’ve just picked up your child’s Kumon homework for Level G1 Reading, and you feel a mix of pride and panic. The passages are getting longer, the vocabulary is more advanced (“foreshadowing,” “inference”), and suddenly, you aren’t sure if the answer is B or C either.

(Level G1) is an exciting milestone. This level is where young learners transition from simply recognizing letters to truly building the foundation for lifelong literacy. Grade 1 Reading Workbook Kumon Publishing

If you don't have the answer book, you might argue B is correct. This is why a parent needs the key. B is a distractor; C is the precise literary evidence.

Moving beyond what is explicitly stated to understand the author's intent.