下列哪种微小生物是没有真正的细胞核的（ ）
A．乳酸菌
B．酵母菌
C．衣藻
D．草履虫
乳酸菌属于细菌，细菌细胞最大的特点就是无成形的细胞核，只有DAN的集中区；酵母菌属于单细胞真菌，细胞内有真正的细胞核；衣藻是单细胞的藻类植物，其内有真正的细胞核，还有一个杯状的叶绿体；草履虫是单细胞的动物，内部有真正的细胞核，一个大核，一个小核．可见A符合题意．
故选：A
Today, February twenty-ninth, is leap day(闰日). This date only appears on the calendar once every four years. But why? Everyone knows the Earth takes three hundred sixty-five days to travel around the sun. Well, that is not exactly correct. The Earth really takes three hundred sixty-five days, five hours, forty-eight minutes and forty-six seconds to complete its orbit around the sun. The problem for people developing calendars was what to do with the extra five hours, forty-eight minutes and forty-six seconds. People needed calendars to help them know when to plant crops and when to celebrate religious holidays. The ancient Greeks and Chinese had a solution. They produced calendars that included extra months every nineteen years. The ancient Romans had a different solution. In the year forty-six, the Roman ruler Julius Caesar made a new calendar. The Julian calendar included an extra day every four years. But there was a problem. The Julian year was just over eleven minutes longer than the cycle of the seasons. In 1582, Pope Gregory the Thirteenth established a new calendar to keep a better recorder of the days. Pole Gregory was the religious leader of most of Europe. He decided that years that could be divided by four would add a day. However, years that ended in two zeros and that could not be evenly divided by four hundred would not be leap years. For example, the years 1700, 1800and 1900 were not leap years. But the years 1600 and 2000 were leap years So leap years are years with three hundred sixty –six days , instead of the usual three hundred sixty –five.This extra days is added to the calendar on February twenty –ninth , sometimes known as leap day .People born on leap day may be called “leapings ”.They usually celebrate their birthday on February twenty –eight or March first . Title: 小题1:
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