sat1两道简单数学题看不懂（囧）,求解（即题是啥意思）

sat1两道简单数学题看不懂（囧）,求解（即题是啥意思）
第一个：
When a certain odd number is divided by 5,the remainder is 1.Which digit must be in the units place of this odd number?
A 1 B 3 C 5 D 7 E 9
啥叫units place啊?
第二道：
Let a "prd" number be defined as one in which the product of the positive divisors of the number,not including the number itself,is greater than the number.Which of the following is a "prd" number?
A 8 B 15 C 18 D 21 E 27
这道题更看不懂了,正除数的积大于本身?
谢谢回答者的回答~