15.在1,2,3,4,5中,能使得代数式(x-1)(x-2)(x+3)(x+4)的值为零的有( )
| A. | 1个 | B. | 2个 | C. | 3个 | D. | 4个 |
13.设n是正整数,则10n+1是( )
0 309702 309710 309716 309720 309726 309728 309732 309738 309740 309746 309752 309756 309758 309762 309768 309770 309776 309780 309782 309786 309788 309792 309794 309796 309797 309798 309800 309801 309802 309804 309806 309810 309812 309816 309818 309822 309828 309830 309836 309840 309842 309846 309852 309858 309860 309866 309870 309872 309878 309882 309888 309896 366461
| A. | n个10相乘所得的积 | B. | 一个(n+1)位的整数 | ||
| C. | 10后面有(n+1)个0的整数 | D. | 一个(n+2)位的整数 |