A piano doesn't like a drum. It doesn't sound like a drum, either(也). So how can the two be alike(相似的) ?

     To play the drums, you use sticks. You hit the drums and the sound comes out. A piano is played in the same way. You hit the keys. The keys move hammers(锤) inside the piano. The hammers hit strings(琴弦) to make sounds. That's how a piano is like a drum.

阻值为3Ω与6Ω的电阻，将它们串联，其总电阻为R₁；将它们并联，其总电阻为R₂，则R₁：R₂等于（　　）

材料1：欧洲可观望阿尔卑斯雪山，且人口在10万以上的城市共有17个，下图是这些城市的分布图。

材料2：2017年3月1日，广州市统计局公布了广州市人口规模及分布情况，广州市常住人口首次超过1400万人，其中外来常住人口533．86万。