— Why does the boy keep crying?
— It is ______ he has lost his favorite car model.
A.since | B.so | C.when | D.because |
The book was written in 1946, the education system has witnessed great changes.
A.when | B.during which | C.since then | D.since when |
My wallet isn’t in my bag. Where I have put it?
A.can | B.must | C.should | D.shall |
Many children may be fond of animals, but ever think of making the study of animals their career.
A.a few | B.few | C.some | D.any |
The country has already sent up three unmanned spacecrafts, the most recent at the end of last March.
A.has been launched | B.having been launched |
C.being launched | D.to be launched |
.______ the satellite launch drawing near, the research workers put their hearts to the test and always stayed up late.
A.As | B.Because | C.With | D.While |