2015年10月19日至23日，******对英国进行了国事访问。中英两国在伦敦发表联合宣言称，两国将共同致力于构建面向21世纪全球全面战略伙伴关系，开启持久、开放、共赢的中英关系“黄金时代”。这表明（    ）

下列词语中划线的字，读音全都不相同的一组是（     ）

曲线y=2sinx在点P（π，0）处的切线方程为 （   ）

    Plastic is easy, convenient, cheap and long-lasting, but it does great harm to the environment.

    Since plastic entered mass production, 8 billion tons have been produced – and we aren't very good at recycling. By 2015, 6,945 tons of plastic waste had formed, with around 9 percent of it getting recycled. About 79 percent of it ends up in landfills or around the environment, including the ocean. We may end up drowning in plastic before long.

    Chemists at Colorado State University have found a polymer（聚酯）that has many of the qualities of plastics – it's light, strong, durable and heat-resistant – but that can be changed back to its original small-molecule（分子）state for complete recycling. Even after being recycled, the polymer can be turned back into its plastic-like state, and this can be done quickly and cheaply.

    This new polymer has all the good qualities of plastics, yet it is relatively easy to make and to recycle. Making it requires room temperature conditions, a short reaction time to bond the monomer（单体）into polymers and only a small amount of the catalyst（催化剂）remains in the end product. It has a high molecular weight, stands up to heat and generally behaves like plastic. Recycling it requires similarly little effort. Mild lab conditions are required and so is a catalyst. Once applied, the polymers are once again monomers in a matter of minutes and can be used to create another product.

    But don't get too excited about this just yet. Scientists stressed that the polymer isn't ready for mass products just yet. There's still plenty of development to do, including making it more economical to produce and recycle.

根据短文理解，选择正确答案。

    A year ago, I paid no attention to English idioms( 习语 ), though my teacher emphasized(强调) the importance again and again. But soon, the importance of English idioms was shown in an amusing experience.

    One day, I happened to meet an Englishman on the road, and soon we began to talk. As I was talking about how I was studying English, the foreigner seemed to be astonished. Gently shaking his head, shrugging his shoulders, he said, “You don't say!” “You don't say!” I was puzzled. I thought, perhaps this is not an appropriate(合适的) topic. “Well, I'd better change the topic.” So I said to him. “Well, shall we talk about the Great Wall? By the way, have you ever been there?” “Certainly, everyone back home will laugh at me if I leave China without seeing it. It was magnificent(宏伟的).” He was deep in thought when I began to talk like a tourist guide. “The Great Wall is one of the wonders in the world. We are very proud of it.” Soon I was interrupted again by his words “You don't say!” I couldn't help asking, “Why do you ask me not to talk about it?” “Well, I didn't request you to do so,” he answered, greatly surprised. I said, “Didn't you say ‘you don't say?'” Hearing this, the Englishman laughed to tears. He began to explain, “‘You don't say' actually means ‘really!'. It is an expression of surprise. Perhaps you don't pay attention to English idioms.” Only then did I know I had made a fool of myself. Since then I have been more careful with idiomatic expressions(习语表达). Remember -- what the English teachers said is always right to us students.