Leave your key with your neighbor ________ you lock yourself out one day.(2012·辽宁)
He stayed up too late every night,______ to catch up with his classmates.
Exercise is _______ as any other to lose unwanted weight.
______known to us,_______ increasing number of students are buried in their studies.
Not until _____,_______the diffiult problem.
She started singing to the baby and was ____ with a smile.