B．Impossible.

　　C．Questionable.

　　D．Suitable.

　　解析：推理判断题。根据末段So I believe technologies like aquaponics are ideal for these kinds of situations.We can actually bring it...in the cities可推断，答案为D项。

　　答案：D

　　4．What is the passage mainly about?

　　A．The future of agriculture.

　　B．Aquaponics and its development.

　　C．The Sweet Water Foundation.

　　D．Aquaponics farms around the world.

　　解析：主旨大意题。本文主要介绍了生态水培技术和这种技术在全世界的发展，故答案为B项。

　　答案：B

　　B

　　We have all heard these words：“just put on a happy face”or“turn that frown upside down”．Can the simple act of smiling actually make us feel better?

　　Our face is formed by a variety of rather thin bones.The muscles that attach to these bones become smaller when we are happy or when we want to laugh.The resulting facial expression is universally recognized as a smile and indicates our positive emotional status.Sometimes，people present fake (假的)smiles.

　　But how does the brain achieve both types of smiles using the same facial muscles？It all depends upon which part of the brain starts the smile.If the brain’s dopamine neurons(多巴胺能神经元)start the smile，then the smile looks sincere.If the brain’s motor cortex starts the smile，in other words，if we are consciously willing ourselves to smile，then a slightly different set of facial muscles are activated.It can be difficult to describe precisely how real and fake smiles differ，but we are all very capable at knowing the difference.But can forcing yourself to smile produce the same kinds of good feelings as a real smile does?

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