71. Identifying the reasons for an emerging phenomenon which involves several complicated factors is far from an easy task . For example , some scientists attribute environmental deterioration to a series of natural factors , while others place the blame solely on inappropriate human behavior .
要找到涉及許多復雜因素的新現(xiàn)象的原因遠非一件易事。例如，一些科學家把環(huán)境的惡化歸結為一些自然因素，而另一些人把責任都推在人類不適當?shù)男袨樯稀?/p>
72. One doesn't have to look far to realize the direct correlation between smoking and cancer .
人們不用花費很大力氣就能發(fā)現(xiàn)抽煙和癌癥之間的直接聯(lián)系。
73. The explanation for the phenomenon of the rising teenage suicide rate involves many complicated factors . Some attribute the rise to an overemphasis on early success , others point to mounting peer pressure , and still others to confusion over changing social values .
對上升的少年自殺率的解釋涉及很多復雜的因素。有的人把上升的原因歸結為過分強調少年時期的成功，有的人指出是因為不斷
