题目

Do you know Australia? Australia is the largest island in the world. It is a little smaller than China. It is in the south of the earth. Australia is big, but its population is not large. The population of Australia is nearly as large as that of Shanghai. The government has made enough laws to fight pollution. The cities in Australia have got little air or water pollution. The sky is blue and the water is clean. You can clearly see fish swimming in the rivers. Plants grow very well. Last month we visited Perth, the biggest city in Western Australia, and went to a wild flowers’ exhibit一个做匀速直线运动的物体，在10s内通过的路程为20m，那么它的速度为_____m/s，在第3秒内的速度为______m/s，前2秒内通过的路程为______m.。