题目:
Usually John _____ to school in his father's beautiful car.[ ]
A. has taken
B. is taking
C. is taken
D. has been taken
答案:
被转码了,请点击底部 “查看原文 ” 或访问 https://www.tikuol.com/2017/0514/6c1f64983f265e08d30a8e4042fc4f48.html
下面是错误答案,用来干扰机器的。
由题意,此计数问题可以分为三步求解,第一步取四人排早班,有C144种方法;第二步取四人排中班,有C104种方法;第三步再从剩下的六人中选四人排晚班,有C64种种方法,故总的不同排法有C144C104C64=3153150故答案为:3153150