Here's why:
* a) marge said train just leaving: This sentence is missing commas and quotation marks, making it unclear who is speaking and what is being said.
* c) thetrain: This is not a sentence. It's just a word.
* d) marge leaving: This is a phrase, not a complete sentence. It also lacks punctuation.
Option b) correctly uses:
* Quotation marks to indicate the words spoken by Marge.
* A comma after "said" to separate the speaker from the speech.
* An apostrophe to show the contraction "is" in "is just leaving."