— Can you tell me ____________?

— In three days.

A．when will they go to the Science Museum

B．how long they have been in New York

C．how soon they will go to see the children left at home

D．what time will they attend the meeting

如图所示，大量氢原子处于能级n＝4的激发态，当它们向各较低能级跃迁时，对于多种可能的跃迁，下面说法中正确的是

A．最多只能放出4种不同频率的光子

B．从n＝4能级跃迁到n＝1能级放出的光子频率最大

C．从n＝4能级跃迁到n＝1能级放出的光子频率最小

D．从n＝4能级跃迁到n＝3能级放出的光子频率等于从n＝2能级跃迁到n＝1能级放出的光子频率