The split between humans and apes is believed by scientists______15 to 20 million years ago.
After the long journey, the three of them went back home, ______.
He _________ to go through the hard times and finally became a famous artist.
It is well known that biology is ______ science about living things.
----May you _______ the experiment! ----Thank you very much.
---Never give up and you'll succeed. ---Thank you. i won't ______ you.