19.为了储存救灾物资,特搭建一长方形库房,经测量长为40m,宽为20m,现准备从对角引两条通道,则对角线的长为( )m.
| A. | 5$\sqrt{5}$ | B. | 10$\sqrt{5}$ | C. | 20$\sqrt{5}$ | D. | 30$\sqrt{5}$ |
18.等腰三角形的一个角是100°,则它的顶角的度数是( )
| A. | 100° | B. | 100°或20° | C. | 100°或50° | D. | 20° |
16.方程x+2y=5的非负整数解有( )
0 294012 294020 294026 294030 294036 294038 294042 294048 294050 294056 294062 294066 294068 294072 294078 294080 294086 294090 294092 294096 294098 294102 294104 294106 294107 294108 294110 294111 294112 294114 294116 294120 294122 294126 294128 294132 294138 294140 294146 294150 294152 294156 294162 294168 294170 294176 294180 294182 294188 294192 294198 294206 366461
| A. | 无数个 | B. | 3个 | C. | 4个 | D. | 5个 |