根据短文内容及首字母提示，填写所缺单词，使短文意思完整。

       Next Friday is Christmas. At this time of the year people usually (1)s            for presents for their families

and friends. They also (2)b            food, greeting cards and Christmas trees before Chritmas. People sing and

(3)d            day and night. And they (4)e            all kinds of food. Many families have Christmas (5)t           .

People decorate them (6)w            coloured lights (彩灯). There are also many (7)p            in the trees. Parents

also put presents in children's stockings (长筒袜). In many places, people think Father Christmas (8)b            

presents to children. He is a fat man in red (9)c           . There is a big (10)b            on his back. In it there are

a lot of presents.

下列函数中是反比例函数关系的是（　　）

A．当速度U=100km/h时，路程S（km）与时间T（h）的函数

B．等边三角形面积S与边长a之间的关系

C．菱形面积一定时，两条对角线a、b之间的关系

D．当梯形的面积S与其上底a一定时，梯形的高H与下底b之间的关系