一箱汽油用掉一半后,剩下的汽油与原来一箱汽油相比较,大小变为原来一半的物理量是( )
A:质量
B:密度
C:热值
D:比热容
读“木桶效应”示意图,完成下题
My friend Tom lives on Sun Street. It is near his school. He usually goes to school on foot. But sometimes he goes to school by bike. His father is a doctor. He goes to work by car. His mother is a teacher. She teaches English. She goes to work by metro. Today is Sunday. Tom doesn't have any lessons. He wants to go to Nanjing by train.
①m1:m2=m3:m4;②m1+m2=m3+m4;③M1+M2=M3+M4;
④M1+3M2=2M3+3M4;⑤m1:m2=M1:M2;⑥m1:m2=M1:3M2.