Earth is believed ______ by an object the size of Mars at some point in the distant past before itssurface cooled.
My father ______ my brother to drive, but my brother wanted to pick ______ the knowledge of the computer during his spare time.
Before he went abroad, he spent as much time as he ______ English.
Even if you are an experienced teacher, you sometimes ______ make some mistakes.
We should know that we can only reach the top if we are ready to ______ and learn from failure.
Young as he is, David has gained ______ rich experience in ______ society.