阅读短文，完成下列问题

Dear Jenny,

   How are you? I am visiting my cousin Howard in Australia. It is hot in Hong Kong but it is cold in Australia in June. When it is summer in Hong Kong, it is winter in Australia. It is snowing heavily now. I like snow a lot and it is a white world outside. I will play with my cousin in the snow this afternoon. We want to make a snowman. I think it is very interesting!

   I like my cousin's house. It is big and there is a beautiful garden（花园）. We can play ball games. My cousin's neighbors are friendly but they cannot speak Chinese. I talk with them in English.

   See you next month.

 Tony

现有开黄色花、红色花、白色花的盆栽月季各一株，请按要求完成下列相应工作。

如图所示，半径为R的半圆柱形玻璃砖某一截面的圆心为O点．有两条光线垂直于水平柱面射入玻璃砖中，其中一条光线通过圆心O，另一条光线通过A点，且OA= $\frac{R}{2}$ ．这两条光线射出玻璃砖后相交于一点，该点到O点的距离为 $\sqrt{3}$  R，求玻璃的折射率．

某《英汉辞典》在解释“bus”时，列出的义项有①公共汽车②火箭的一级③火车车厢④公共马车。如果按照历史上这些含义出现的先后来编写辞条，那么正确的排序应当是(  )