Option 'a' correctly uses commas to separate items in a simple list. No colon is needed before a simple list that directly follows the verb. The provided activity question 3 also confirms this as the correct answer.
Class 6 › English Grammar and Composition › Chapter 8: Punctuation & Capitalisation › Topic: Comma usage (independent clauses, introductory words, additional information, serial comma, geographical names, dates, addresses, titles)
Aligned to the NCTB national curriculum.