连一连。

如图所示将若干个点摆成三角形图案，每条边（包括两个端点）有n（n＞1，n∈N^*）个点，相应的图案中总的点数记为a_n，则 $\frac{9}{a_2{a}_3}$ + $\frac{9}{a_3{a}_4}$ + $\frac{9}{a_4{a}_5}$ +…+ $\frac{9}{a_{2015}{a}_{2016}}$ =（  ）

    It's six forty in the morning. The children are coming into the classroom.

    A girl is opening the windows. Some are laughing and talking. Some are listening to them. Some are reading books. Some are doing their homework.

Miss Lin is standing behind the teacher's desk. She is writing on the blackboard. Sue and Anna are wearing their new dresses today. Ann is cleaning her desk. Mike is helping her. They all look happy.

    What are Bill and Bob doing? Oh, dear! They are still playing basketball.

杜甫《登高》中，感慨自己离家万里又年老多病的诗句是：“____， ____。”