. There's no bus now, and we can't get home _______ by taxi.
It was in the street ______ I live that I met Mr. Green.
A man may usually be known by the books he reads _______ by the friends he keeps.
There are so many books! It is not easy for us to decide what to take and what to_______.
When I try to understand _______ that prevents so many Americans from being as happy as one might expect, it seems to me that there are two causes.
The science of medicine, _______ progress has been very rapid lately, is perhaps the most important of all the sciences.