题目

阅读理解     People usually talk about two groups of colours: warm colours and cool colours. Scientists think that there are also two groups of people: people who prefer warm colours and people who prefer cool colours.    The warm colours are red, orange and yellow. Where there are warm colours and a lot of light, people usually want to be active(活跃的). People think that red example is exciting sociable (善交际的) people, those who like to be with others like red. The cool colours are green, blue and purple. These colours unlike warm colours, are relaxing. Where there（2002•崇文区）如图，菱形ABCD的边长为5，AC、BD相交于点O，AC=6，若∠ABD=α，则下列式子正确的是（ ）A．sinα=B．cosα=C．tanα=D．cotα=