(2018邯郸二模)You must treat your school work seriously ________ you want to go to the key senior high school.
A.unless B.if C.though D.because
(2018秦皇岛二模) My mother has taught in this school ________ our family moved to this city.
A.for B.until C.because D.since
(2018张家口桥西区一模)It was dark at that time, ________ I couldn't see what had happened.
A.and B.but C.or D.so
(2018石家庄一模)We should give the boy another chance ________ he has made a mistake.
A.though B.when C.unless D.because
(2018云南)We don't know the love of our parents ________ we become parents ourselves one day.
A.until B.after C.when D.since
(2018沈阳)My grandparents wrote letters to keep in touch with others ________ they were young.
A.when B.since C.after D.before