题目

D As I was reading a recent story in Slate on 20-somethings complaining about how the economy was ruining their life plans, I couldn’t help but think the 20-somethings sounded like a bunch of spoiled children who grew up expecting everything to be easy for them. As a 20-something myself, I certainly share their disappointment: my husband and I probably won’t be able to buy a house until we’re in our 40s, and we too are burdened by student loans(贷款). But why should it be any different? Being young persons in America, shouldn’t they take up all of the challenges and opportunities tha如图所示，光滑水面上放置质量分别为m和2m的四个木块，其中两个质量为2m的木块间用一根不可伸长的轻绳相连，木块间的最大静摩擦力是2μmg．现用水平拉力F拉其中一个质量为m的木块，使四个木块以同一加速度运动，则轻绳对2m木块的最大拉力为（ ）A．B．C．D．8μmg