Fivepersonsaretravelingwithtwoluggagebags.Everytime,
needtwoofthemtocarrytheluggagetheybagsandtheydolikethisinturnduringthetravel.Now,theyhavewalked15km.
Question:Howmanykilometersdideachtravelwithaluggagebagonwalk?
Answer:___________
A.15kmB.7.5kmC.6kmD.30km
并说明选择答案的理由