A:①②
B:③④
C:①③
D:②④
Replacing some things in your house at the right time can make you healthier. Some researches show us when and why the following things should be replaced.
Word Box: wool羊毛 dry-clean 干洗 bacteria 细菌
注:图中,E表示能量,p表示压强,t表示时间,V表示体积.