began to grow on land.They were followed in time by land animals.Some were insects.Others, \s\up1(32(32)called amphibians\s\up1(33(33)， were able to live on land as well as\s\up1(34(34) in the water.Later when the plants grew into forests, reptiles\s\up1(35(35) appeared for the first time.They produced young generally by laying eggs\s\up1(36(36).After that, some huge animals, called dinosaurs\s\up1(37(37)， developed.They laid eggs too and existed\s\up1(38(38) on the earth for more than 140 million years.However, 65 million years ago the age of the dinosaurs\s\up1(39(39) ended.Why they suddenly disappeared\s\up1(40(40) still remains a mystery.This disappearance made possible the rise of mammals\s\up1(41(41) on the earth.These animals were different from all life forms in the past, because they gave birth to\s\up1(42(42) young baby animals and produced milk to feed them.

　　⑳unlike/ʌn'laIk/ prep.与......不同；不像

　　\s\up1(21(21)fundamental/ˌfʌndə'mentl/ adj.基本的；基础的

　　be fundamental to是......的基础

　　\s\up1(22(22)It was not immediately obvious that ..., it为形式主语，that引导的从句为真正的主语。

　　\s\up1(23(23)the continued presence of water 水的长期存在

　　continued adj.持续不断的

　　presence/'prezns/ n．出席；到场；存在

　　\s\up1(24(24)dissolve/dI'zɒlv/vt.&vi.溶解；解散

　　\s\up1(25(25)harmful/'hɑːmfl/ adj.有害的

　　be harmful to对......有害(＝do harm to)

　　\s\up1(26(26)acid/'æsId/ n．酸

　　\s\up1(27(27)a chain reaction连锁反应

　　chain/tʃeIn/n.链子；连锁；锁链

　　in chains戴着镣铐

　　reaction/rI'ækʃn/ n．反应；回应

　　\s\up1(28(28)multiply/'mʌltIplaI/vi.&vt.乘；增加

　　\s\up1(29(29)oxygen/'ɒksIdʒən/ n．氧

　　\s\up1(30(30)encourage vt.鼓励；激励；促进；激发

\s\up1(31(31)shellfish/'ʃelfIʃ/n.水生有壳动物