Here's the answer:
“냉장고에 우유가 얼마나 있어요?”
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 97.54% of the time!
Fun fact: the hundreds of thousands of people learning Korean with Memrise get this phrase correct 97.54% of the time!