tailieunhanh - Cracking the Toefl IBT 2009 edition part 47

Cách dễ nhất để đăng ký cho TOEFL là tham dự các kỳ thi trực tuyến. Bởi vì xét nghiệm là dựa trên internet, thời gian thử nghiệm nhiều hồ quang sẵn có, mặc dù điều này không nhất thiết phải thật sự ở nước ngoài. Hãy chắc chắn rằng bạn đăng ký sớm để bạn nhận được một thời gian thử nghiệm và vị trí mà bạn cảm thấy thoải mái . | 21. According to paragraph 5. how did daguerreotypists prevent the production of blurred images during exposure A They exposed the plates for shorter lengths of time. B They instructed their customers not to blink. C They had special furniture for their customers to use. D They allowed their customers to take short breaks. Paragraph 5 is marked with an arrow i l Only a small number of professional photographers ever had any practical experience as daguerreotypists. those technicians who made photographs through the daguerreotype process By its strictest definition the daguerreotype process was common for not more than 20 years in the mid-1800s Other ways ol making photographic images on metal plates such as tintypes and ferrotypes were developed rapidly after the advent of the daguerreotype They quickly eclipsed it in popularity. Today the surviving photographs produced by these methodsafe often referred to as daguerreotypes but that designation is incorrect It is not surprising that photography enthusiasts began looking for alternatives to the daguerreotype almost immediately The materials it required were both expensive the plates contained silver and one ot the developing solutions contained gold and extremely risky Strict adherence to proper laboratory procedure was necessary in order Io avoid poisoning by noxious gases The steps involved in preparing and exposing a daguerreotype were as laborious and frustrating as they were hazardous Images were recorded on copper plates to which several thin coats of silver had been applied. After being fastened to wooden blocks the plates were scoured with alcohol and squares of soft flannel Since even one speck ol dust could easily create a deep enough groove to render the final image worthless they had to be perfectly buffed. The plates were then bathed in solutions ol bromine and iodine. The thin layer ol bromo-iodine that formed on them made them sensitive Io light al which point they were ready lor exposure Alter .