(2017河北34题)Mom won't let Dick go out ________ he promises to be back by 10：00 tonight.
A.if B.when C.since D.unless
Bob, dinner is ready. Please wash your hands ________ you eat.
A.until B.after C.while D.before
Be more careful and more patient, ________ you will make fewer mistakes in the following experiments.
You can either email us ________ come to our office for your questions.
My arm is still painful, I'm going to see a doctor.
A.so B.for C.but D.or
Tony used to be a quiet student, ________ now he is active in class.
A.so B.and C.but D.or
