Alice: Hi, Frank! Are you free on Saturday?

Frank: Yes.____

Alice: I heard a baby panda was born in the zoo. Let's go and have a look.

Frank: Oh, I have been there twice. I think you'd better learn something about pandas before you go to the zoo.

Alice: I know a little.____There are about 2,000 pandas living in the forests.

Frank: That's true. They are in danger now.

Alice: Why? Is it because they don't have babies very often?

Frank:____ Another main reason is that humans cut down lots of bamboo forests, and pandas don't have enough food to eat.

Alice: That's too bad !____

Frank: We can make some posters to tell people to save pandas.

Alice: I will take some photos of the pandas first when I visit the zoo.

Frank:____Have a good time!

Alice: Thank you.

阅读下边的示意图，造成图示现象的外部条件主要在于（      ）

    Every weekend is important to the Franklin's family. During the week they don't have very much time together, but they spend a lot of time together on the weekend.

    Mr. Frankin works at the shoe store downtown during the week, but he doesn't work there on the weekend. Mrs. Franklin works at the city hospital during the week, but she doesn't work there on the weekend.

    Bobby and Sally Franklin go to the junior high school during the week, but they don't go there on the weekend.

    And the Franklin's dog Rover stays at home alone during the week, but he doesn't stay at home alone on the weekend.