20
(A) care
(B) careful
(C) cared
(D) carefully

very+adj.   careful 

very只能接形容詞

The typical American throws away about 590 kg. of garbage a year. For the nation as a whole, this _____16_____ 160 million tons of waste a year, or enough to make a chain of 10-ton garbage trucks halfway to the moon. In the early 1990s, Japan recycled about 50% of its trash; the U.S. only about 10%, _____17_____ estimates of the U.S. Environmental Protection Agency. In modern recycling plants, _____18_____ can handle the metals and the glass, but people must separate the plastic by hand, so when people put out the garbage, they must separate the recyclable _____19_____ the non-recyclable materials. Recycling is not a new idea. In emergencies like droughts and wars, people have recycled all kinds of materials and have been very _____20_____ about how much water and electricity they used. Today we must protect our planet Earth by bringing back the old habit of recycling.