某种细菌在培养过程中,每20分钟分裂一次(一个分裂为两个),经过3个小时,这种细菌由1个可繁殖成[ ]
A、511个
B、512个
C、1023个
D、1024个
答案:B
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Families in big cities have ()children than they did thirty years ago.
《道路交通安全法实施条列》有关高速公路的规定中规定标明的最高车速不得超过时速()公里。
A.110
B.120
C.130
D.140