Old papers can 20 be used to line rubbish bins and as packing material when mailing breakable goods.
答案：(B) also
also（也）表示「舊報紙也可以被用來……」，承接前文列舉的其他用途，屬於累加式列點。soon（很快）、thus（因此）、rather（相當）都不符合這種「還可以用來做……」的累加語意。
四個選項都是副詞，都能擺在 can 與 be 之間，你會憑中文挑一個。
這是邏輯勾環，線索一定要跨句才看得到。前面已經列了兩項舊報紙的用途：做成木炭、拿來擦窗戶與鏡子。空格這一句 Old papers can ______ be used to line rubbish bins and as packing material（舊報紙______可以拿來墊垃圾桶、當包裝材料）講的是第三項用途，是在同一份清單上再加一項。表示累加，用 also。填進去讀成 Old papers can also be used to line rubbish bins。順帶留意它的位置：also 是副詞，習慣擺在助動詞 can 之後、主要動詞之前，這是課本教過的固定位置。
soon（很快）講的是時間，這一句沒有時間先後的問題；thus（因此）要求後面是前面造成的結果，但第三項用途不是前兩項造成的；rather（相當地；寧可）擺在這裡兩個意思都接不上。
also（也，擺在助動詞之後、主要動詞之前）、as well（也，擺在句尾）、too（也，擺在句尾）、be used to V（被用來做某事）、line a rubbish bin（在垃圾桶內側鋪一層）、packing material（包裝材料）。
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.