His brother aims to be __________ of his parents by the time he is twenty.
The book _______ forty maps, _______ that of Great Britain.
I know nothing about the young lady _______ she is from Beijing.
Scientists say it may be five or ten years _______ it is possible to test this medicine on human patients.
I send you 100 dollars today, the rest _______ in a year.
Taking a plane is the quickest _______ to get to Tibet.