观察图，请将下列事件发生地点的英文字母代号填入图中相应方框内。

A、粉碎德军“不可战胜”神话的战役地点：莫斯科

B、开辟打击德国法西斯第二战场的登陆地点：诺曼底。

Hello! My name’s John. I’m in Beijing now. It’s hot in Beijing. It’s sunny too.

I can wear my shorts and shirt. My shorts are green. I have a new jacket. My old jacket is too small. I want to buy a hat.The hat is very pretty, but it is $60. that’s very expensive.

The hat is cheap.

两艘潜艇相距S，以相同的速度v₁成单纵队同向航行，后艇的超声定位器发出信号到达前艇并被反射回来，声音在水里传播的速度等于v₂，则后艇发出信号和收到回声两时刻之间的时间间隔为　____ ．