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在房間門口東瞧瞧西望望。細心地亞萍馬上意識到客人在找服務(wù)員,她立即過去有禮貌地向客人問好:“下午好,先生!您有什么事需要我?guī)兔?？”客人這時開口:“你們酒店是怎么搞的,天氣這么冷,連空調(diào)都沒開,是不是空調(diào)壞了？”客人滿口怨氣對著亞萍?！拔铱梢赃M房間檢查一下嗎？”亞萍面帶微笑地說?！班?。”經(jīng)得客人同意,亞萍隨客人進了房間,看到空調(diào)的開關(guān)到“OFF”狀態(tài),連忙對客人說:“對不起,先生。未能詳盡介紹房間內(nèi)設(shè)備的使用方法是我們工作未做好,請您原諒。”邊說著邊打開空調(diào)至“1”檔。這時徐徐暖風飄出來?？腿烁杏X游客暖氣,煉說謝謝! 問題:（）我們從中得到什么啟發(fā)？

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.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 synthesizeDC．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 chromosomE．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 chromosomeD．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 inheritancE．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 diseasE．