21. That matters because theory suggests that the maximum sustainable yields that can be cropped from a fishery comes when the biomass of a target species is almost 50% of its original levels.
【分析】多重復合句。句子主干是 That matters。because 引導原因狀語從句，其中又包含 that 引導的從句作 suggests 的賓語。賓語從句主干為 the maximum sustainable yields...comes...，其中又嵌套 that 引導的定語從句修飾主語 yield，另外還包含 when 引導的時間狀語從句。
【譯文】這一點很重要，因為理論認為目標物種的生物量達到原始基數的50%左右時，從漁場中才能夠獲得最大的可持續產量。
【點撥】crop 作名詞時，意為“莊稼；收成；產量；一群，一批”。作動詞時，意為“收獲，獲得；減短”，此外，還有短語 crop up“出現或發生（尤指意外地）”。

22. But somewhere from the 19th century onward, more artists began seeing happiness as insipid, phony or, worst of all, boring as we went from Wordsworth's daffodils to Baudelaire's flowers of evil.
【分析】復合句。句子主干為 more artists began seeing happiness as...，其中使用了 see...as...結構。句首短語 somewhere from the 19th century onward 作時間狀語；為時間狀語從句 as we went from...to...。
【譯文】但到了19世紀的某個時期，更多的藝術家開始將快樂視為索然無味、矯揉造作——甚至更糟的是——令人厭倦的東西。從華茲華斯的《水仙花》到波德萊爾的《惡之花》就可以表明這一變化。
【點撥】1)insipid “枯燥乏味的”。2)phony“虛偽的，虛假的”。