Mary: What are you going to do this weekend, Lucy?

Lucy:____much. How about you, Mary?

Mary: I'm going to buy my father a present for his fortieth birthday. Would you like to go with me?

Lucy: I'd love to, but where would you like to go shopping?

Mary:____place where they have many different stores.

Lucy: I hear a new shopping center just opened downtown.

Mary: That____great. What time would be good for you?

Lucy: How____2:30?

Mary: Sure. That would be fine.

Lucy: Where should we meet, then?

Mary :____meet just outside the shopping mall.

Lucy: OK. See you then.

Mary: See you.

已知数列{a_n}是无穷等比数列，其前n项和是S_n，若a₂+a₃=2，a₃+a₄=1，则$\underset{n\to \infty }{\lim }{S}_n$的值为（　　）