This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
[{'content': 'Which of the following techniques can extend the working time of a zinc phosphate cement? \nSelect and explain. \nA. The P/L  ratio  can  be  reduced  to produce a thinner mixture, B. Smaller portions of powder should be mixed for the first few increments, C. Colder mixing temperature (though temperature of mixing slab should be above dew point), D. All of the above', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Control of Setting Time:\nManufacturing process\n\nSintering temperature:\xa0Higher the\xa0temperature, the more slowly the cement sets.\nParticle size: Finer particles react more quickly as a greater surface area is exposed to\xa0the liquid.\nWater content of liquid: Presence of excess water accelerates, whereas insufficient water\xa0retards the reaction.\nBuffering agents: When added,\xa0slows down the reaction.\n\nFactors under control of operator\n\nTemperature: Higher temperatures accelerate the reaction. Cooling the mixing slab is an effective way of slowing the\xa0reaction and prolonging the working time.\nPowder-liquid ratio: More the liquid, slower the reaction.\xa0\nRate of addition of powder to liquid: The reaction is slower, if the powder is incorporated slowly.\nMixing time: Longer the mixing time (within practical limits), the slower is the rate of reaction.\n\nRef: Manappalil P: 90', 'role': 'assistant'}]