恩格斯说，罗马法“是商品生产者社会的第一个世界性法律”。对这句话的正确理解是（   ）

已知数列$\left\{a_n\right\}$中，$a_1=1$前n项和为S_n，且点$P\left(a_n,a_{n+1}\right)\left(n\in N^{*}\right)$在一次函数y=x+1 的图象上，则$\frac{1}{S_1}+\frac{1}{S_2}+\frac{1}{S_3}+...+\frac{1}{S_n}=$（   ）

    Christmas is coming. Stephen can see it everywhere he 1 There are Christmas things to sell in the shops and Christmas trees in the park. But it is only in late 2 . Stephen thinks this is wonderful. He likes Christmas very much. To celebrate it for a month is not enough.

     He went into a clothes shop to buy 3 . He found a perfect (完美的) pair.

    "Just these, sir?" asked the shop assistant.

    "Yes, please," 4  Stephen.

    "They look a little big for you. Are you sure they will 5 ?" asked the shop assistant.

    "Oh, they will be fine," said Stephen,

    It was 6 the trousers were a little big. But they  7  to be. Every Christmas Stephen 8 as Father Christmas and works in the local shopping mall. Children like to take photos with him.

    Stephen walked out of the 9 and smiled happily. What 10 he do this Christmas?

52－30=____