下图为直流电源，为浸透饱和氯化钠溶液和酚酞试液的滤纸，为电镀槽．接通电路后发现上的c点显红色。为实现铁上镀铜，接通后，使c、d两点短路。下列叙述正确的是(　　)

设数列{a_n}的前n项和为S_n，已知a₁=1， $\frac{2S_n}{n}=a_{n+1}-\frac{1}{3}{n}^2-n-\frac{2}{3}$ ，n∈N^*．

阅读理解
    Hello, my name is Lina. I'm 10 years old. I'm wearing a red dress. Red is my favourite colour and dresses are my favourite clothes. I like to read books. Fish is my favourite food. Amy is my friend. She is 11 years old. She likes green and her favourite clothes are skirts. She likes to play ping­pong. She likes fish, too. But her favourite food is rice and vegetables. We like to drink juice.

水与我们的生活息息相关，下列有关水的物理量间的关系图线中，正确的是（  ）

秦统一后，在全国范围内建立了强大的中央集权制度。权力的高度集中，成为秦朝政治制度的基本特征。权力高度集中的标志表现为（  ）