The parents suggest_________in the hotel room but their kids were anxious to camp out

during the trip.   [ ]

A. sleep                      

B. to sleep    

C. sleeping                    

D. having slept

NO是大气污染物，但少量NO在人体内具有扩张血管，增强记忆功能。NO难溶于水，通常条件下极易与O₂。则实验室收集NO的方法为                        

A．向下排空气法    

B．向上排空气法  

C．排水集气法    

D．以上方法都可以