单项选择题
Just as I was leaving the house， it occurred （）me that I had forgotten my keys.
A.on B.in C.at D.to
单项选择题 Aprofessor，alongwithsomestudents，（）nowworkinginthenewlaboratory.
单项选择题 Smithregretted（）tothemeetingyesterday.
单项选择题 （）isasolutiontotheproblemofwatershortage，wehavetoputalloureffortstogether.
