Final answer:
Commas should be placed to clarify the separation of items in a list and between independent clauses in compound sentences. Serial commas add clarity in lists, and commas should not follow subjects or verbs unless needed in compound sentences.
Step-by-step explanation:
Comma Placement in Sentences
Correct comma usage is essential for the clarity and flow of a sentence. Here are the sentences with the necessary comma placement:
My mother took me to the market, ballet studio, and public library.
I finally found my keys, and I got to work just in time.
Mrs. Contreras threw out her old coffee table and cleaned the carpet.
Taking the elevator to the roof, we hoped we could see the skyline and the bay.
Though Susan wasn't feeling well, she went to the store anyway and bought ice cream, pizza, and candy.
I let my neighbor borrow my phone because she said hers was tapped by the police.
Remember that serial commas (also known as Oxford or Harvard commas) should be used for clarity in a list of items. Also, do not place commas directly after subjects or verbs unless they are part of a compound sentence requiring a comma before a conjunction such as 'and' or 'but' when connecting two independent clauses.