题干
Betty, still ______ excited, took away the box ______ with birthday presents for her.
A：looked; filled
B：looked; filling
C：looking; filled
D：looking; filling
答案(点此获取答案解析）
C
是表面积为
的球面上的四点，且AB、AC、AD两两互相垂直，则
的面积之和
的最大值为
