根据对话内容，在空白处填入恰当句子，使对话完整、通顺

A. Hi ken! Are you busy now?

B: Yes I'm a little busy.

A: ?

B: I'm thinking about shopping for a birthday gift for my sister online.

A: ?

B: No. I never shop online so I don't know how to do that.

A: Oh, I shop online all the time.

B: ?

A: I think it's faster and the things online are cheaper.

B: OK. Come and help me. Let's look at my computer together.

A: ?

B: I want to buy a book.

A: OK. First, let's find a website (网站). Lots of sites sell books.

B: OK, sounds good.

A: ？

B: Books about history. My sister likes reading them.

A: OK. Let's look for history books.

B: Wow! There are lots of books. How can I choose just one?