I don't understand why if I did the answer in present continious you take it as a mistake. We are seeing the apple.
Because it is a mistake.
We don't generally use "see" in the -ing form in English when we talk about observing something with our eyes.
Only in metaphorical uses, e.g. "I am seeing his daughter" which means "I go out on dates with his daughter".
http://ebooks.edu.gr/modules/ebook/show.php/DSDIM-B100/497/5206,23935/ (search for "stative verbs")