A.2π/3
AC=2倍根号2,
△ACD1的高=根号6
△ACD1截球O的截面圆的半径:
=(根号2:根号6)×根号2
=2:根号6
截球O的截面圆的面积:
=(2:根号6)×(2:根号6)×π
=2π/3