We are learning English, but how can we learn English well? A student can know a lot about English, but maybe he can not speak English.
If you want to know how to swim, you must get into the river. And if you want to be a football player, you must play football. So , you see, you can learn English only by using it. You listen to your teacher carefully in class. You must read your lessons every day. You must speak English to your English teacher and classmates and also you must write in English. Then one day, you may find your English very good.

多项式2a²b-ab²-ab的项数及次数分别是（　　）

已知 $\frac{\text{x}}{8}$ =1.2， $\frac{8}{y}$ =1.2，则x和y比较（  ）

如图，小虎用水平向右的力推放在水平地面上的箱子，但没有推动，则此时（　　）

已知铝的密度为2.7×10³kg/m³．，相对原子质量为 27，阿伏加的罗常数为6.0×10²³mol^﹣1，则铝原子的直径为____，体积为0.17m³的铝块中的原子数为____．