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　　1. 指代：指代词(it，they，this，these，other，another，such，the)必向前指代。

　　(1)THIS+V+XXX

　　例题1：

　　Impacts by meteorites represent one mechanism that could cause global catastrophes and seriously influence the evolution of life all over the planet. █According to some estimates, the majority of all extinctions of species may be due to such impacts. █Such a perspective fundamentally changes our view of biological evolution. █The standard criterion for the survival of a species is its success in competing with other species and adapting to slowly changing environments. █Yet an equally important criterion is the ability of a species to survive random global ecological catastrophes due to impacts.

　　Look at the four squares [█] that indicate where the following sentence can be added to the passage.

　　This is the criterion emphasized by Darwin's theory of evolution by natural selection.

　　Where would the sentence best fit?