One question per week) (Issue 1)
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This post was last edited by yanran88 on 2010-12-11 at 15:18. Given that everyone has limited time and energy, the daily question format has been changed to a weekly one. Everyone is welcome to participate; please hide your replies, as replies posted after the answers are revealed will not be scored. Thank you for your cooperation! Hidden method: http://bbs.hcbbs.com/thread-492556-1-1.html; please do not edit after replying. 1. As the diameter of a plate tower increases, the cost per unit volume ( ) ； As the diameter of the packed tower increases, the cost per unit volume decreases. A. Decrease, increase B. Increase, decrease C. Increase, increase D. Decrease, decrease 2. For steel with medium hardness, the Brinell hardness value is approximately ﹙﹚ times the Rockwell hardness value. A. 4 B. 6 C. 8 D. 10 3. What determines the type of an element is the （ ） in its atoms. A. Number of protons B. Number of neutrons C. Number of electrons D. Number of neutrons and electrons 4. Which of the following changes is a physical change? A. Straw hats bleached with sulfur dioxide turning yellow over time B. Solid ammonium chloride vaporizing when heated C. White phosphorus emitting light in the dark D. Solid iodine vaporizing when heated 5. The maximum direct current value that a person can withstand on their own is ﹙﹚. A. 20mA B. 30mA C. 40mA D. 50 mA
1、A； 2、D;3、C ； 4、D ； 5、D
1. For plate towers, as the tower diameter increases, the cost per unit volume (B)； As the diameter of the packed tower increases, the cost per unit volume decreases. A. Decrease, increase B. Increase, decrease C. Increase, increase D. Decrease, decrease 2. For steel with medium hardness, the Brinell hardness value is approximately ﹙D﹚ times the Rockwell hardness value. A. 4 B. 6 C. 8 D. 10 3. What determines the type of an element is the （A） in its atomic structure. A. Number of protons B. Number of neutrons C. Number of electrons D. Both the number of neutrons and electrons 4. Which of the following changes is a physical change? (D) A. Straw hats bleached with sulfur dioxide turning yellow over time B. Solid ammonium chloride vaporizing when heated C. White phosphorus emitting light in the dark D. Solid iodine vaporizing when heated 5. The maximum direct current that a person can withstand on their own is ﹙A﹚. A. 20mA B. 30mA C. 40mA D. 50 mA
1.A 2.D. At medium hardness levels, the relationship between Rockwell hardness HRC and Brinell hardness HBS is approximately 1:10; for example, 40HRC is equivalent to 400HBS. 3.A 4.D 5.D
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