Answer: The answer would be "he said that New York's restaurants are great, that it's parks are beautiful, and that it's population is diverse.
Explanation: They reason why that is the correct answer is because when you use commas in a sentence they are meant to be a substitute for the word AND. Also you wouldn't want it to be repetitive like saying "He said that" " And that" or "That the population is".
Answer:
What do you need help with? If it's an essay or something, I'm not too good at those, but I still would like to lend a hand :)