ordinal product

例句：

1. 1.The first-year students are required to take a comprehensive exam.
   一年级学生必须参加综合考试。
2. 2.The ordinal product of 4 and 5 is 20.
   4和5的序数积是20。
3. 3. The ordinal product of 7 and 8 is 56.
   7和8的序数积是56。