.The reason why she was upset was _____ her son didn't pass

.The reason why she was upset was _____ her son didn't pass the final exam.
A.that
B.so
C.why
D.because
Before the final examination,many students have shown __C___ of tension.Some have trouble sleeping while others have lost their appetite .
A.anxiety
B.marks
C.signs
D.remarks
We had intended to do everything according to the schedule,but it didn't _____ as planned.
A.make up
B.turn out
C.go on
D.come up
A series of debates between the major candidates _____ scheduled for the Labor Day weekend last week.
A.is
B.are
C.was
D.were
（怎样区别ATER 做连词和介词?例如：
6.After ___C__ seemed hours of waiting in line,finally it was our turn to pass the gateway.
A.that
B.it
C.what
D.as
我要具体的解答.