有这样一道立体几何选择题:四个侧面是全等等腰三角形的四棱锥,其底面是:(A)正方形;(B)矩形;(C)菱形;(D)以上结论都不是.并给出正确答案为(C).此题近来已作为较为流行的测试题,而且一般都是根据以下解法来选择答案的. There is such a three-dimensional geometric multiple-choice question: four sides are all isosceles triangular pyramids, the bottom surface is: (A) square; (B) rectangular; (C) diamond; (D) none of the above conclusions. And give The correct answer is (C). This topic has recently been used as a more popular test topic, and it is generally based on the following solution to choose the answer.