数学prep两道题求教，谢谢

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19.        2463-!-item-!-187;#058&002761

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

7.         905-!-item-!-187;#058&000575

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, then 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

 终于重新编辑好了

19.        2463-!-item-!-187;#058&002761

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
     

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答案是3吗，如果是的话就是说有几对前后连续的数乘积为负数。

那就是1，-3和-3，2和5，-4

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答案是3吗，如果是的话就是说有几对前后连续的数乘积为负数。

那就是1，-3和-3，2和5，-4

第一题选c，第二题选e么？

1.问相邻两数乘积为负的数有几对？显然有3对，1×-3，—3×2，5×-4

2，原式=2^50×（1×2×3×……×50）+1

所以h（100）+1除以任何小于50的数都余1

所以p>50

大概是这样吧～