20. _______, English is one of the most important subjects.
| A．It is known to all that | B．As is known to all that |
| C．As we know | D．As it is known to all |
It wasn’t long _______ the two daughters of President Obama got used to the life in the White House
A that B before C until D and
that Marie was able to set up new branches elsewhere.
| A．So successful her business was |
| B．So successful was her business |
| C．So her business was successful |
| D．So was her successful business |
My parents live in a small village. They always keep candles in the house_____there is a power out.
| A．if | B．unless | C．in case | D．so that |
Leave your key with a neighbor _______ you lock yourself out one day.
| A．ever since | B．even if | C．soon after | D．in case |
Small sailboats can easily turn over in the water ______ they are not managed carefully.
| A．though | B．before | C．until | D．if |