问题 问答题 简答题

如果你利用生牛乳通过细菌自然发酵制造能饮用的酸牛乳,应控制在哪一时期?

答案

参考答案:从牛乳酸败过程中细菌的生态演变过程来看,生牛乳的状态经历了几个阶段的变化:1、牛乳PH中性,含丰富的乳糖——>乳酸PH下降;2、引起蛋白质结块———>抑制了乳链球菌的繁殖3、乳杆菌能耐受低PH,发酵乳糖————>PH更低4、酵母菌在这低PH环境下利用乳酸生长———>乳糖、乳酸消失,PH上升;5、假单胞菌、芽胞杆菌能产生蛋白酶,分解凝结的牛乳蛋白,当蛋白质被利用完毕,牛乳的分解也就完成了

选择题
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Recently I paid a visit to Harvard University, where there are top class scientists and professors and the best academic system in the world.

I was pretty shocked when I first stepped onto the campus. Well, it's not even really a campus. It's more like a district in a small town.

Harvard's main buildings are from the 18th century. They look very old and simple. You might even say they're a little shabby. They don't fit the modern idea of university at all. The buildings are surrounded by grass and trees, so I felt as if I had walked into a medieval castle. But when I looked across the street, busy shops and in-fashion students made me feel like I was in the 21st century again. It creates a strong contrast and brings a special atmosphere to the school.

Our tour guide Gary took us around and told us: "You see this grass field in the center of the school? Here is where they host their graduation ceremony. They just set up tents and benches and have a very simple ceremony. Unbelievable! Who would think the most talented students just graduate on the lawn?

I saw some students put a blanket on the grass and lie down to read a book. When I listened to the soft sound of pages turning, along with chirping of the birds, I felt very calm. There was no competitive feeling at all.

Harvard has the world's first computer in its science center and there are hundreds of high-end computers too. Its religion and the literature departments are also among the best. It is the perfect mix of tradition and new technology. It makes Harvard a very attractive place to study in.

I hope one day I'll attend my dream school—Harvard.

45.The article is mainly about        

A.the author's campus life in Harvard     B.the author's impression of Harvard

C.Harvard's old buildings                              D.the academic system at Harvard

46.The author was most impressed by        , according to the article. 

A.Harvard's mix of tradition and new technology

B.the classes held on beautiful lawns at Harvard

C.Harvard students not taking their graduation ceremony seriously

D.the feeling of not living in modern society on the campus

47.What can we conclude from the article? 

A.Harvard campus is actually a district of a big city.

B.There are no competitions at Harvard University.

C.Graduation ceremonies are not complex at Harvard.

D.All Harvard buildings date back to the 18th century.

48.According to the article, in which fields is Harvard top in the world? 

A.Literature, arts, and law.              B.Religion, law and arts.

C.Literature, arts and computer science.   D.Religion, computer science and literature.