对比实验是运用比较的方法来揭示事物的性质或变化规律的一种实验方法。课本中设计的下列实验属于对比实验的是（  ）

镁是一种用途很广的金属，从海水中提取镁的主要步骤如图所示，请你和他一起探究．

用所给动词的适当形式填空，完成短文

 Children’s Safety

I ____(talk) to some students. I ____(ask) about safety rules when they ____(be) younger. Their rules were very good.

John ____(say), “I couldn’t play in the kitchen.” His mum and dad didn’t ____(like) that.

Jennifer ____(can) play the piano and she could also ____(play) games in the living room. When her mum and dad ____(not, be) home, she couldn’t cook.

Tom could play in the bedroom or the living room. He couldn’t ____(play) in the bathroom or the kitchen.

What ____(be) your safety rules when you were young? ____(talk) to younger students about these and ____(help) them.