题目

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。 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. The population of Australia is nearly as large as that of Shanghai. The cities in Australia have got little air or water pollution. 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' exhibition. There we saw a large number 6．下列函数中，最小正周期为π的是（　　）A．y=|sinx|B．y=sinxC．sin3xD．y=cos4x