17.已知单项式-xm-2y3与$\frac{2}{3}$xny2m-3n是同类项,那么m,n的值分别是( )
| A. | $\left\{\begin{array}{l}{m=3}\\{n=-1}\end{array}\right.$ | B. | $\left\{\begin{array}{l}{m=3}\\{n=1}\end{array}\right.$ | C. | $\left\{\begin{array}{l}{m=-3}\\{n=1}\end{array}\right.$ | D. | $\left\{\begin{array}{l}{m=-3}\\{n=-1}\end{array}\right.$ |
14.下列事件是必然事件的是( )
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| A. | 太阳从西方升起 | B. | 打开电视正在播放《新闻联播》 | ||
| C. | 若a≤0,则|a|=-a | D. | 某运动员投篮时连续3次全中 |