【Weekly Question】Participate from 6/12 to 6/18, 2017 for +2 wealth； +3 to +10 wealth for correct answers

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To increase the popularity of the chemical analysis section, a \"Question of the Week\" campaign has been launched to foster an active atmosphere for technical exchanges while providing rewards in the form of financial benefits to users. 【Weekly Question】Multiple-choice question: In the qualitative test for thiols in light petroleum products (Drabek test), which of the following ( ) phenomena indicates that the sample has passed the test. A. After the first shaking for 15 seconds, a brown precipitate forms slowly. B. After adding sulfur powder and shaking for 15 seconds, no brown or black precipitate forms after resting for 1 minute. C. After removing hydrogen sulfide from the sample, add sulfur powder and shake for 15 seconds; an orange-red color will appear after 1 minute. D. If no change occurs after the first shaking, the sample can be declared “pass”. Answer: B. Reply with your answer in the comments to participate; you will receive +2 wealth points. If you answer all questions correctly, you’ll get an additional +3 to +8 wealth points. Those who provide thorough analyses and explanations for the questions (or include detailed calculation processes) will receive extra wealth points as a reward. If your answer is correct and your analysis is accurate, it will be marked as the best reply (or the best assistance). Feel free to answer the questions.