Some environmental scientists suggest turning newspapers 16 charcoal.
答案：(A) into
【句型】turn A into B 固定搭配，表示「把 A 轉變成 B」；for／off／upon 都不是 turn 表達「轉變」的正確搭配介系詞。
turn 後面能接的介系詞很多——turn on、turn off、turn down、turn to——你會憑印象挑一個最眼熟的。
先確認空格前後各是什麼：前面是 turning newspapers（把報紙變成……），後面是 charcoal（木炭）。這是一個「A 變成 B」的結構，起點是報紙、終點是木炭，而標出終點的介系詞是 into。turn A into B 是成組的說法。填進去讀成 turning newspapers into charcoal（把報紙變成木炭）。同一組的說法可以一起記：change A into B、transform A into B、translate A into B，介系詞一律用 into——指考 99 年第 13 題考的 transform sunlight into electric power（把陽光轉換成電力）就是同一個結構。
turn off（關掉）後面接的是電器或開關；turn for 不是成立的組合；turn upon 雖然存在（turn upon somebody 突然翻臉攻擊某人），主詞要是人或動物，而且與「變成什麼」完全無關。
turn A into B（把 A 變成 B）、change A into B（把 A 改變成 B）、turn to somebody for help（向某人求助）、turn off（關掉）、stack up（堆積起來）、a substitute for（……的替代品）。
If old newspapers are stacking up in your house, there are options other than tossing them out or selling them to a recycler.
Some environmental scientists suggest turning newspapers 16 charcoal. This can be done by soaking sheets of newspaper in water for two hours and then 17 them into small pieces. These pieces are then compressed into balls. After the water is 18, the ball-shaped pieces are put under the sun to dry before they can be used as a firewood or charcoal substitute.
19 suggestion made by the experts is to dip newspaper sheets in vinegar and water, and use them to clean windows, mirrors, and tiles. Old papers can 20 be used to line rubbish bins and as packing material when mailing breakable goods.