2.若$\left\{\begin{array}{l}{x=2}\\{y=-1}\end{array}\right.$是二元一次方程组$\left\{\begin{array}{l}{2x+y=m}\\{x-ny=3}\end{array}\right.$的解,则m,n的值为( )
| A. | 3,1 | B. | 3,-1 | C. | -3,1 | D. | -3,-1 |
17.
如图是由一水桶抽象而成的几何图形,其俯视图是( )
| A. | B. | C. | D. |
16.-2,0,0.5,-$\sqrt{2}$这四个数中,属于无理数的是( )
0 283177 283185 283191 283195 283201 283203 283207 283213 283215 283221 283227 283231 283233 283237 283243 283245 283251 283255 283257 283261 283263 283267 283269 283271 283272 283273 283275 283276 283277 283279 283281 283285 283287 283291 283293 283297 283303 283305 283311 283315 283317 283321 283327 283333 283335 283341 283345 283347 283353 283357 283363 283371 366461
| A. | -2 | B. | 0 | C. | 0.5 | D. | -$\sqrt{2}$ |