A:孔乙己
B:寿镜吾老先生
C:藤野先生
D:范爱农
Hello,friends! My name is Jack.I am a Chinese boy.My favourite food is chicken.I like beef noodles,too.I don't like fish but egg is OK.Potatoes are my favourite vegetable.My favourite fruit is bananas.They are so sweet.
如图,从地面上C,D两点望山顶A,测得它们的仰角分别为45°和30°,已知CD=100米,点C位于BD上,则山高AB等于( )
可见光的波长范围为( )