题目内容
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[单选题]
RP （Received Pronunciation) refers to a way of pronouncing standart English that is used by 2% of the————population.
A.USA
B.PRC
C.UK
D.AU
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发布时间：2022-01-07
题目内容
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第1题
The step angle of stepping motor is 0.1°, the frequency of control pulse is 6kHz, the rotation speed of the motor is rpm.
第2题
Cells have several ways of ensuring that their daughters remember what kind of cells they should be. How do differentiated cells maintain their identity?
A．One of the simplest and most important is through a positive feedback loop, where a master transcription regulator activates transcription of its own gene,in addition to that of other cell-typespecific genes. Each time a cell divides, the regulator is distributed to both daughter cells, where it continues to stimulate the positive feedback loop.?The continued stimulation ensures that the regulator will continue to be produced in subsequent cell generations.?Positive feedback is crucial for establishing the “self-sustaining” circuits of gene expression that allow a cell to commit to a particular fate—and then to transmit that decision to its progeny.
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B．Although positive feedback loops are probably the most prevalent way of ensuring that daughter cells remember what kind of cells they are meant to be,there are other ways of reinforcing cell identity. One involves the methylation of DNA．In vertebrate cells, DNA methylation occurs on certain cytosine bases. This covalent modification generally turns off the affected genes by attracting proteins that bind to methylated cytosines and block gene transcription. DNA methylation patterns are passed on to progeny cells by the action of an enzyme that copies the methylation pattern on the parent DNA strand to the daughter DNA strand as it is synthesizeD
C．Another mechanism for inheriting gene expression patterns involves the modification of histones. When a cell replicates its DNA,each daughter double helix receives half of its parent’s histone proteins, which contain the covalent modifications that were present on the parent chromosom
E．Enzymes responsible for these modifications may bind to the parental histones and confer the same modifications to the new histones nearby. It has been proposed that this cycle of modification helps reestablish. the pattern of chromatin structure found in the parent chromosome
D．Because all of these cell-memory mechanisms transmit patterns of gene expression from parent to daughter cell without altering the actual nucleotide sequence of the DNA,they are considered to be forms of epigenetic inheritanc
E．These mechanisms, which work together, play an important part in maintaining patterns of gene expression, allowing transient signals from the environment to be remembered by our cells—a fact that has important implications for understanding how cells operate and how they malfunction in diseas
E．
第3题
Please translate the English sentence into Chinese. They provide everything for themselves. They make their own electricity, they pump their own water, they cut the forest logs to build their cabins.
第4题
In the UK, which country is the smallest of all the 4 countries, both in population and area?
A、Northern Ireland
B、England
C、Wales
D、Scotland
