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
— Why didn’t you try to finish the composition?
— I tried to, but ________ I could, the bell ran announcing the end of the examination.
A.until B.when
C.after D.before
—Have you known each other for long?
—Not very long, ________ we started to work in the company.
A.after B.before C.when D.since
The doctor shares his phone number with the patients ________ they need medical assistance.
A.if only B.as if C.even though D.in case
________ birds use their feathers for flight, some of their feathers are for other purposes.
A.Once B.If C.Although D.Because
（2015·福建） the students came from different countries, they got along quite well in the summer camp.
A. While B. Unless
C. Since D. Until
