A:has been designed
B:had been designed
C:was designed
D:would be designed
一个数增加二成后是4.8,那么这个数是____。
为了探究影响电热的因素,小伟设计了如图所示电路,烧瓶中盛有质量、初温均相等的煤油,R甲>R乙。