If an integer n is to be selected at random from 1 to 105, inclusive, what is probability n(n+1) will be divisible by 7?	Choose the correct choice from the following choices.
A) 1 / 7  B) 3 / 14  C) 1 / 2  D) 2 / 7  E) 3 / 4

Rationale: "for n ( n + 1 ) to be a multiple of 7 , either n or n + 1 has to be a multiple of 7 . thus n must be of the form 7 k or 7 k - 1 . the probability is 2 / 7 . the answer is d ."
Answer: D