Here's the answer:
“可以啊”
(ké-yǐ a)
Watch a real native speaker say it:
Here's how it sounds in a textbook:
You could also say:
- kéyǐa
- nǐ ké-yǐ a
Fun fact: the hundreds of thousands of people learning Chinese with Memrise get this phrase correct 90.54% of the time!