分式 $\frac{a}{6b^{2}c}$ ， $\frac{b}{3a^2{c}^2}$ ， $\frac{c}{4ab}$ 的最简公分母为____．

雌蛙的卵巢中有初级卵母细胞6000个，从理论上计算，经减数分裂所生成的卵细胞和极体数分别是（　　）

下列关于和平共处五项原则的说法，不正确的是(    )

    Today is Friday. Peter has six classes today. He goes to school at 7:30 a.m. At 8:00 a.m., he begins his first class. The first class is English. At 9:00 a.m., he has math. Peter likes math because it’s interesting. At 10:00 a.m. she has a biology class. Peter thinks it's very boring. Then at 11:00 a.m., he has a history class. That's his favorite subject. He can learn a lot about the past from history.
    Peter has lunch at school at about 12:00. Then he has a short break. At 1:30 p.m., he has a music class. At 2:30 p.m., he has a P.E. class. Peter likes this afternoon, because music and P.E. are easy and interesting. School is over at 4:00 p.m. Peter is happy because he can go home and have a good time on Saturday and Sunday.
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中学时代，是生命历程中的一个重要支点，这是因为中学时代（  ）

①是人生发展的一个新阶段                           ②为我们的一生奠定重要基础

③见证着一个人从少年到青年的生命进阶   ④是人生最美好的年华