_______ of the area _______ covered by trees.
A：Two-third; is
B：Two thirds; is
C：Two-third; are
D：Two thirds; are
“元起朔方，固以崇尚释教，及得西域，世祖以地广而险远，……思有以因其俗而柔其人，乃郡县吐蕃之地，设官分职，而领之于帝师。”这里的“官”隶属于（ ）
