【单选题】Li Lei didn't come to school today. What _______ to him? [ ]
【单选题】矿物表面润湿接触角与矿物的可浮性关系,接触角小,则矿物的(),难浮。
【单选题】I don't know____yesterday. [ ]
【单选题】I didn't know what ____ to her last night. [ ]
【单选题】-----What _____? -----I______my key and can't open the door.
D.
has happened, have lost