The boy ____ lost his backpack has to borrow books from his teachers.
A：whose
B：who
C：whom
D：which
下列区域叙述正确的是（ ）
秦岭﹣﹣淮河一线以北的主要植被类型是（ ）
分别阐述固态、液态和气态物质的特点．
