Here's the answer:
“제 조부모님께서는 젊었을 때 아프리카에 가셨어요”
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 95.54% of the time!
Fun fact: the hundreds of thousands of people learning Korean with Memrise get this phrase correct 95.54% of the time!