根据你的生活与学习经验，对代数式 2（x+y）表示的实际意义作出两种不同的解释．

下图是表示气体微粒的粒子模型，图中“○”和“●”分别表示氧原子和氢原子．其中能保持氢气化学性质的是粒子模型是（   ）

Paul: Hey, Jenny, the subject for my school project is "Small invention that changed the world". Can you help me think of an invention?

Jenny: With ____! Let me think ... hmm ... I know! The zipper!

Paul: The zipper? Is it ____ such a great invention?

Jenny: Think about how often it's used in our ____ lives. You can see zippers on dresses, trousers, shoes, bags ... almost everywhere! I saw a website last week. The ____ of different inventions were listed there. For example, it mentioned that the zipper was ____ by Whitcomb Judson in 1893. But at that time, it wasn't used widely.

Paul: So when did it become popular?

Jenny: Around 1917.