Choose the sentence with correct punctuation and the correct rule.
a. When he stepped on the banana peel he slipped and fell. NEEDS NO COMMAS
b. When he stepped on the banana peel, he slipped, and fell. ITEMS IN A SERIES
c. When he stepped on the banana peel, he slipped and fell. DEPENDENT CLAUSE
d. When he stepped on the banana peel, he slipped and fell. NON-RESTRICTED APPOSITIVE