BBC ESL-Word master

I studied words at BBC ESL. It has three levels and I chose medium first. I think I can answer midium levet, but I can't. It is hard to think a word as a English than I think. So I chose easy level and I can answer. Sometimes I didn't know the answer, then, I clicked 'definition of the word'. So I finished easy level! I think it is easy to answer what 'apple' is. But it is difficult to answer what 'red fruit that has a lot of vitamin C'. Do you agree with me?