【提出问题】切开的苹果“生锈”与什么因素相关？

【猜想与假设】

猜想①：可能与空气没有关系，只是果肉内的物质自身相互反应而“生锈”

猜想②：可能是果肉中的物质与空气中的氧气作用而“生锈”

猜想③：可能是果肉中的物质与空气中的氮气作用而“生锈”

猜想④：可能是果肉中的物质与空气中的二氧化碳作用而“生锈”

    Jim, Tom and Tim are in the park. It's a small park, but it's nice. They can see some animals there. There are some birds in the tree. They are yellow. They can fly high. Quack… Quack… What do you hear? Oh，Some ducks. They can swim in the water. There are seven white ducks and nine black ducks. What's that? It's a cat. It's under the tree. It's white. It can jump very fast. The children like the small animals very much.

①雄赳赳、气昂昂，跨过鸭绿江

②还我山东，还我青岛

③打倒蒋介石，解放全中国

④稻谷堆得圆又圆，社员堆稻上了天。撕片白云擦擦汗，凑上太空吸袋烟