Final answer:
The sentence correctly punctuated is b) 'Sam Gold said, "A verbal contract isn't worth the paper it's written on."' This is the correct use of quotation marks and period placement in American English.
Step-by-step explanation:
The correct sentence that is punctuated properly is option b). This sentence correctly uses double quotes to indicate the exact phrasing of what Sam Gold said, with the period inside the quotation marks, which is grammatically correct in American English. In option a), there is a use of the word 'that' after 'said,' which is unnecessary in direct quotations. In option c), the quotation is incomplete since it lacks the closing quotation marks. Therefore, only option b) successfully uses both a signal phrase and the correct punctuation for the quotation.
Editing for more effective sentences involves eliminating unnecessary words and phrases, correcting punctuation, and refining the sentence structure to enhance clarity and readability. It is important to know the rules for integrating quotes into your text, which includes using the correct punctuation and clear attribution through signal phrases.