今日长难句
That matters because theory suggests that the maximum sustainable yield that can be cropped from a fishery comes when the biomass of a target species is about 50% of its original levels.（Text3. 2006）
maximum / ˈmæksiməm / adj.最多的；最大极限的
sustainable / səˈsteinəbl / adj.可持续的
yield / ji:ld / n.产量；产出；利润
crop / krɔp / v.有收成
fishery / ˈfiʃəri / n.渔场
biomass / ˈbaiəumæs / n.生物量
target / ˈtɑ:ɡit / n.目标；指标
species / ˈspi:ʃi:z / n.物种
original / əˈridʒənl / adj.原来的；起初的
结构分析
你需要知道
本句为嵌套结构。主干That matters后接原因状语从句because...，原因状语从句中嵌套宾语从句that the maximum sustainable yield...comes，宾语从句中又嵌套了一个定语从句that can be cropped from a fishery.和一个时间状语从句when the biomass...。
翻译
而这很重要，因为理论认为当目标物种的生物量大约为其原始水平的50％时，从渔场能够获得最大的可持续产量。
预告明日长难句
Today, surrounded by promises of easy happiness, we need art to tell us, as religion once did, Memento mori: remember that you will die, that everything ends, and that happiness comes not in denying this but in living with it.（Text4. 2006）
