16. 以下哪个数可以等于the difference between two prime numbers. 貌似选项有7,11,9…
11 since we have 2 and 13 as prime numbers. 9 since we have 2 and 11.
Note: All prime numbers are odd except 2. So the difference between all prime numbers except 2 are even. Only when you compare 2 with another prime number, you can get a difference as an odd number.