Here's the answer:
“그들은 더 이상 서로 말하지 않아요”
Watch a real native speaker say it:
Here's how it sounds in a textbook:
Fun fact: the hundreds of thousands of people learning Korean with Memrise get this phrase correct 90.24% of the time!
Fun fact: the hundreds of thousands of people learning Korean with Memrise get this phrase correct 90.24% of the time!