Today is my birthday. I am a girl. My name is Han Mei. I'm nine years old. I have a birthday party. I have a birthday cake and many gifts. My father and my mother say“Happy birthday!”to me. I'm very happy.
下图是某地地形图,MN、PQ是地形剖面线。①、②是水库,若从中选择一个作为自来水厂的水源地,其条件是自流引水且工程建设费用最小。完成下列小题。