— I seem to be lost. Could you tell me ______?

— Sure. You can take the No.3 bus to get there. [ ]

A. where is the nearest hospital

B. how long it will take me to the airport

C. how far is my trip to the Olympic Village

D. how I can get to the National Museum

流行病学实验研究不具备的特点是

A．需随机化分组

B．必须有干预措施

C．实验组和对照组是自然形成的

D．有严格的平行可比的对照

E．是前赡性研究