单选题 A chess king is said to attack all the squares one step away from it, horizontally, vertically, or diagonally. For instance, a king on the center square of a 3 × 3 grid attacks all 8 other squares, as shown below. Suppose a white king and a black king are placed on different squares of a 3 × 3 grid so that they do not attack each other. In how many ways can this be done?
国际象棋中的国王可以沿水平､垂直或对角线方向攻击与它一步之遥的所有方格。例如，如下图所示，3 × 3 方格表的中心方格内的国王可以攻击到其他 8 个方格。假设一个白色国王和一个黑色国王被放置在 3 × 3 方格表的不同方格上，使得它们互相不攻击。问满足这样要求的放置方式有多少种？