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【单选题】
That a person could live in the modern world without synthetic substances is probably possible, but whoever tried to do it would soon miss many common things. (46) Just imagine how many varieties of plastics there are. They can be harder than wood or .softer than rubber. They can even be made resistant to fire, water and electricity. Whoever visits the world's market places will find that plastics are being made and used everywhere. Plastic articles can be produced at a rather low cost. The machines for molding them are not large or heavy. Most of the products can be stored and transported easily. (47). As a matter of fact, many kinds of materials for clothing have plastics in them. They are made of plastic fibres and are known by special names such as nylon or dacron. Clothing made of plastic fibres has certain advantages over that of natural fibres like cotton, wool, or silk. (48). (49) The earliest variety of plastics was called 'celluloid'. It appeared on market over a hundred years ago. In 1912, an American scientist presented to the world a hard plastic material known as 'bakelite'. The 1940's saw a faster development of plastics. An even larger variety of plastic materials came into practical use. Now plastics find wide application not only in our daily life, but also in engineering. The Germans have manufactured a car which is almost completely made of plastics. The famous British engine builders have produced an aeroplane engine made mostly of plastics. It is really true that plastics are for everyone. And the fact that the total volume of plastics in use is on the increase suggests that more and better plastics will be made in the near future.(50).
A.
Besides plastic pens, combs and tooth brushes, he would be without many kinds of cloth as well as some necessary parts for radios and television sets.
B.
The history of plastics is longer than you might expect.
C.
That's why factories for making them can be found in many countries.
D.
The former is lighter in weight, easier to wash and dry, keeps in shape much longer and does not wear out so quickly.
E.
It is not likely that plastic fibers will compelely take the place of natural fibers.
F.
Perhaps we could call it the Plastic Age.
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【单选题】原核生物 RNA 聚合酶核心酶由( )组成。
A.
2αββ′ω
B.
2α2ββ′ω
C.
2αββ′ωσ
D.
2α2ββ′ωσ
【判断题】鸟类上下颌骨极度前伸,构成鸟喙,鸟喙外具角质鞘,构成锐利的切缘或钩,是取食器官。()
A.
正确
B.
错误
【简答题】若已知两个同频率电压的有效值相量分别是 则电压 。
【判断题】0机舱发生火灾时,对受火灾威胁的空气瓶,应采取排气降压措施,以防爆炸。( )
A.
正确
B.
错误
【多选题】原核生物的RNA聚合酶 ( )
A.
全酶由α 2 ββ′ωσ 组成
B.
核心酶由α 2 ββ′ω组成,催化RNA链延长
C.
σ亚基识别转录的起始点,然后催化转录过程
D.
能催化与模板互补的2个相邻NTP间形成3’,5’磷酸二酯键
【多选题】原核生物的RNA聚合酶
A.
]全酶由α 2 ββ′ωσ 组成
B.
]核心酶的各亚基均能单独与DNA结合催化转录
C.
]核心酶由α 2 ββ′ω组成,催化RNA链延长
D.
]σ亚基识别转录的起始点,然后催化转录过程
E.
]能催化与模板互补的2个相邻NTP间形成3’,5’磷酸二酯键
【单选题】[9-9]The master shall be ___ the marine environment when taking collision-avoiding action.
A.
Aware of
B.
Clear of
C.
In charge of
D.
Interested with
【单选题】原核生物中, DNA 指导的 RNA 聚合酶由数个亚基组成,其核心酶的组成是
A.
α2ββ′ω
B.
α2ββ′ωσ
C.
α2β′
D.
α2β
E.
αββ′
【单选题】已知两个同频率电压的有效值相量分别是 ,则电压 ( ) V 。 A.10 B.20 C.30 D.50
A.
10
B.
20
C.
30
D.
50
【单选题】原核生物DNA指导的RNA聚合酶由数个亚基组成,其核心酶的组成是
A.
α2ββ′ω
B.
α2β′δω
C.
α2β′ω
D.
α2β′ε
E.
α2ββ′ωδ
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