Which of these sentences uses quotation marks correctly?

“If you would all quiet down.” He said, “I will explain what we will do next.”

“If you would all quiet down” he said “I will explain what we will do next.”

“If you would all quiet down” he said, “I will explain what we will do next”.

“If you would all quiet down,” he said, “I will explain what we will do next.”

A is wrong because it has a period after, down when it should be a comma. The comma signals that that part of the sentence is what he is saying. He is also capitalized when it should be lower case. B is wrong because it has nothing after, down and nothing after said. C is wrong because again, there's nothing after down. The part option C did get right is the comma after said. D has all the commas in the right places and all the words are capitalized when they're supposed to.