Here's the answer:
“나는 잠시 생각이 필요해요”
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 93.58% of the time!
Fun fact: the hundreds of thousands of people learning Korean with Memrise get this phrase correct 93.58% of the time!