When to use comma and period on a sentence?

Use a period at the end of a sentence. You typically use periods when your declaring something.

Examples: I like pizza. I am going to Hawaii next summer.

Use a comma in several different circumstances such as before a coordinating conjunction (FANBOYS), adding on to a sentence, and typically where you want the reader to pause and take a breath.

Example: My favorite sports are football, basketball, and volleyball.

When it is raining you should use an umbrella, or you will get wet.  

the correct answer is (a) . answer should be simple, clear and brief.