题干

某同学欲从土壤中分离出能分解尿素的细菌并对该菌进行计数,下列实验操作中不正确的是(  )

A:将土壤用无菌水进行一系列的梯度稀释

B:在无氮培养基中加入酚红指示剂可用来鉴定分解尿素的细菌

C:可将未接种的培养基在相同条件下培养作为对照

D:同一浓度的土壤稀释液应至少涂布三个平板

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B

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    Death of science icon(巨匠)

    In modern history, there has perhaps never been a scientist as well-known as Stephen Hawking. Whether he was educating the world with his knowledge of the universe(宇宙), or making fun of himself in TV shows like The Simpsons, it's hard to imagine what the world will be like but now Hawking is no longer in it.

    On March 14, the British physicist passed away at his home in Cambridge, England. Since then, many people have expressed their sadness in public, including British computer scientist Tim Berners-Lee, who invented the World Wide Web. “We have lost a great mind and a wonderful spirit,” Berners-Lee wrote.

    Hawking was an icon for many reasons, but he will be best remembered for his work in the field of science. Building on German scientist Albert Einstein's work, Hawking explained his belief that space started with the Big Bang, and will end with Black Holes. This idea kicked off a series of scientific studies including into the origin of the universe itself.

    Besides his work in science, he also managed to overcome many difficulties in his personal life. While studying at Cambridge University, he got a serious illness at the age of 21. His illness left him disabled and he was told he only had a short time to live. However, as we all know, he went on to become one of the greatest minds that the world has ever known.

    Hawking leaves behind a great legacy(遗产). His book A Brief History of Time: From the Big Bang to Black Holes that came out in 1988, became one of the world's best-sellers. He may no longer be with us, but Hawking will continue to inspire the world for generations to come. As he once said himself, “Look up at the stars and not down at your feet.”

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