表中的生态系统的净初级生产力不同。 以净初级生产力增加为序排列表中的生态系统（） ["③、⑥、②、⑤、④和①","③、⑥、⑤、②、④和①","⑥、③、⑤、②、④和①","⑥、③、②、⑤、①和④"]
装潢设计恰到好处的包装是“无声的推销员”，这体现了包装的（）作用。 ["保护商品","方便运输","增加价值","促进销售"]
依据《工作票管理规定》，需要将高压设备停电的电气工作及热力机械工作，应使用（）票。 ["一种票","二种票","停电票","口头命令"]
To make sure of getting the full advantage of a favorable current，you should reach an entrance or strait at what time in relation to the predicted time of the favorable current?（） ["One hour after the predicted time","At the predicted time","30 minutes before flood，one hour after an ebb","30 minutes before the predicted time"]
液化石油气分离得到的（）可以用来生产合成塑料。 ["甲烷","乙烯","乙烷","丁烷"]
两段煤气炉与单段煤气炉的主要区别有哪些？
