一道GMAT数学题,求高人指教.

题目

一道GMAT数学题,求高人指教.
For a finite sequence of nonzero numbers,the number of variations in sign is defined as the number of pairs of consecutive terms of the sequence for which the product of the two consecutive terms is negative.What is the number of variations in sign for the sequence 1,-3,2,5,-4,-6
(A) One
(B) Two
(C) Three
(D) Four
(E) Five

答案

C
the number of variations in sign的定义是那些相邻(consecutive)两项乘积为负的数的对数(pairs)
观察知道1,-3; -3,2; 5,-4; 这三组数成立