下列实验操作中正确的是（ ）
| A．应使混合物中的水分完全蒸干后,才能停止加热 | |
| B．蒸馏操作时，应使温度计水银球靠近蒸馏烧瓶的支管口处 | |
| C．分液操作时，下层液体从分液漏斗下口放出后再将上层液体从下口放出到另一个烧杯中 | D．萃取操作时,应选择有机萃取剂,且萃取剂的密度必须比水大 |
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