题目

I got nervous when the woman _____ opposite kept staring at me.    A. seat   B. to seat   C. seating   D. seated 答案：D（2007•北京）如果正数a，b，c，d满足a+b=cd=4，那么（ ）A.ab≤c+d且等号成立时a，b，c，d的取值唯一B.ab≥c+d且等号成立时a，b，c，d的取值唯一C.ab≤c+d且等号成立时a，b，c，d的取值不唯一D.ab≥c+d且等号成立时a，b，c，d的取值不唯一