如图为人体消化系统的部分结构示意图．下列叙述正确的是（　　）

    Three kids have been learning chemistry for only a few months. But they have already begun to challenge (挑战) a world famous scientist!
Li Weichi, Huang Runling, and Xiao Yan are from Zhongshan Huaqiao Middle School in Guangdong. They have just found a red cabbage that could be a new kind of acid-base indicator (酸碱指示剂). They want it to take the place of litmus (石蕊) paper.
    "We've learnt to think of and ask questions about life by ourselves," said Li, "We work well with each other."
    British scientist Robert Boyle discovered the use of litmus paper over 300 years ago. Now it is used widely in experiments all over the world.
    But when the kids did some experiments in class last winter, they saw that the litmus paper didn't turn very blue with base matter. It's hard to get a clear result.
    Will there be a better indicator than litmus paper? The three kids decided to try and find out!
    How? They went to collect over 40 plants in parks, gardens and markets. Then they ground (研磨) leaves, flowers and stems (茎) to get the pigments (色素) from them.
    The kids mixed pigments with acid and base. They spent months watching carefully to see which paper showed the best color change. They decided it was the litmus paper!
    "It's our first scientific journey, Huang said, "But it makes me want to try harder."

    Humans like to live and work in groups. Language is the “cement(胶合剂)”____holds these groups together. Language is part of culture. Culture, in this sense,____ (mean) all those customs, skills, and attitudes that are part of the behavior of a ____ (particularly) group. What you think ____ what you want in life are all affected by the culture of the group in which you ____( raise). Groups of people live in different ways. They may have different skills, organizations, and art forms. Their family life may be completely different from yours.

    Human beings are inventive animals. They can decide to change their cultures in order to meet various ____(situation). Of all living things, human beings are the ____(clever). They can choose ____(live) in many environments and in a wide variety of ways. Only human beings can choose where and how they want to live and then improve the physical environment to help ____(they)realize these choices.

    Acquiring the wisdom to make wise choices ____ (be)the lasting challenge of being human.

牙齿对动物的生存和生活具有重要意义，生活在南极的海豹在冰下游泳时，隔一段时间就要用牙齿咬破坚冰，浮出水面呼吸空气，海豹牙齿的损坏即意味着死亡的来临．人的牙齿损坏以后，不仅影响食物的消化，而且会引起疾病，给人带来极大的痛苦．如图是某动物上、下颌骨及牙齿的示意图，请据图回答下列与牙齿有关的问题．