That's fun to say. tokk tokk

I never know when to choose clever and smart

What's difference between smart and clever?

Of course.

女子아이가 똑똑합니다

Why is it "ga" and not "neun" for the ending of girl?

I noticed Rosetta stone uses the ending 해요 instead of 니다. It's my understanding that it is infact less formal; would the reason they use it instead, then be, because it's more common while still being respectful?