43 What did Dr. Hernandez and his team look for to detect signs of trouble in sewers ?
(A)hydrogen
(B) hydrogen sulphide  
(C)carbon dioxide 
(D) hydrogen dioxide 

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統計： A(13), B(208), C(28), D(20), E(0) #982456

詳解 (共 2 筆)

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A candidate, Dr. Her...
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One of the hidden glories榮譽 of Victorian engineering is proper drains降低；消耗. Isolating a city’s effluent廢水，污水 and shipping船舶, 運輸 it away in underground sewers下水道；排水管 has probably saved more lives than any medical procedure程式；步驟；常規 except（表示不包括）除…之外 vaccination接種疫苗.
But out of sight超出支付能力的, 極好 is out of mind精神錯亂，發狂, 犯傻.
And that, together with the inherent內在的；固有 yuckiness令人讨厌 of the subject, means that many old sewers下水道；排水管 have been neglected and are in dire need of repair. If that repair does not come in time如期而至, the result is noxious（尤指氣體或其他物質）有毒的，有害 and potentially hazardous危險. All this neglect疏忽照顧；忽視, though, makes it hard to know where best to apply the sticking枝條；木條-plasters灰泥，灰漿. So Mark Hernandez of the University of Colorado, Boulder, and his team have been looking for an easily measurable signal that something is about to go wrong.  
A candidate申請人；候選人, Dr. Hernandez suspected認為可能, 懷疑, is hydrogen sulphide硫化氫. This is one of the gases that make sewage污水；汙物 stink氣味, 散發異味，發出難聞的氣味.
Though not itself damaging to a pipe’s fabric布；織物, 結構, it can be converted轉變, （使）改變 by certain species of bacteria into sulphuric硫酸 acid.
Pretty well all sewage污水；汙物 smells of hydrogen sulphide硫化氫  though, so for it to be a useful telltale洩露秘密的, 告密者，打小報告 you need to know just how much is a sign of trouble.
Dr. Hernandez and his colleagues therefore因此，因而 collected samples from 36 sewers下水道；排水管 in various states of decay腐蝕；（使）衰敗 and started looking.  
One of their interests was in the mixture of bacteria found in pipes in different states of repair.
Rather than culturing these, a process to which not all species are amenable易接受建議的；耳朵軟, they ran them through a mass DNA screening that shows up everything in a sample.
They also measured the acidity酸的含量，酸度 of the sewage污水；汙物 soaked into濕透的，浸透 the pipe wall near where the sample was collected and recorded the concentrations in the air there of hydrogen sulphide硫化氫  methane甲烷，沼氣 and carbon dioxide二氧化碳.
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