----- Oh, my goodness! My laptop must have got stolen． ----- But where _____ a thief have entered the house with all the doors and windows still locked?

It is important to know about the cultural differences that______ cause problems．

Though the girl had been suffering from the blood disease, she acted as if nothing____ to her while facing her friends and relation.

(2013·陕西高考)The children ________ lost in the woods; otherwise, they would have been at the lakeside camp as scheduled.

If only he _____ quietly as the doctor instructed, he would not suffer so much now.