For every positive even integer n, the function h(n) is defined to be the product of all the even integers from 2 to n, inclusive. If p is the smallest prime factor of h(100)+1, the p is

a. between 2 and 10

b. between 10 and 20

c. between 20 and 30

d. between 30 and 40

e. greater than 40

h(100)=2*4*6*8*10*.....*100 质因子 1 2 3 5 7 。。。37 都是h(100)的因子

所以这些因子都不是h(100)+1的因子 So p is greater than 40

精辟！加一点，h(100)的质因子最大为47，所以p 大于40

tip: h(n)+1 prime factors if exist, shall > n/2 (n is a positive even number)