1.Which of the following staetments is true about chemical nutrients in an ecosystem? a.They flow through the system,losing some nutrients in the process. b.They cycle within the ecosystem,being constantly reused. c.They can be converted into energy. d.They depend on sunlight as their source. e.They cannot be obtained from decomposition. Ans:b b我能接受但一开始是写d... 可是又遇见了第二题...有矛盾? 2.The chemical energy used by (most) organisms for metabolism and growth ultimately comes from ______. a.heat b.the decomposition of plants c.the sun d.carbon dioxide e.evolution Ans:c 和第一题有矛盾? 所以我写了a... 3.Scientists discard a model when ______. a.new experimental results are obtained that cannot be explained by the old model b.the old model has been in place a long (旧的被长时间取代就丢弃 好像对..) c.the individuals who first developed the old model have died (新个体被发展出来 旧的死亡 是这个意思吗?) d.no experiments related to the model have been done recently (没有实验再与此model有关联 所以舍弃 好像也对...) e.all of the above Ans:a 每个选项看起来都正确@@ 我选e... 4.In some places a polypeptide may coil or fold back on itself.This is call _____,and the coils or folds are held in place by ____. a.tertiary stucture...covelent bonds b.secondary structure...hydrogen bonds Ans:b a.b配对都没问题 套进去看来也都合理... --

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