Final answer:
The number between 31 and 100 is 45 (option 3).
Step-by-step explanation:
To find the number between 31 and 100, we need to look for a number that is greater than 31 but less than 100. From the given options, the number that fits this criteria is 45 (option 3). This number falls between 31 and 100 and is the only option provided that satisfies the condition.