Answer:
The two independent clauses are:
Grandpa Simpson smiled to himself
he was about to win the game
Step-by-step explanation:
Independent clauses are complete sentences, which means that if you take away the rest of the sentence, that part will make sense on its own. A complete sentence consists of at least a subject and verb.
For example, if we remove "he was about to win the game" from the sentence, the first part would still make sense. This means the first part, "Grandpa Simpson smiled to himself," is an independent clause. We have a subject, Grandpa Simpson, and a verb, smiled.
The same applies to the second part of the sentence, which reads, "he was about to win the game". If we remove everything but that part, the sentence is still complete with a subject and and verb, which means it is an independent clause.