潮汐池里的动物: mussel,barnacle, sea anemone,sea spider,octopus, sea cucumber, abalone, hermit crab, sea star 潮汐池的危险: the way the water moves,drying out 海星的身体部位: spiny skin,eyespots,tube feet, arms,mouth 指示代词的用法，例如: this,these 副词的用法，例如: safely 介词的用法，例如: in,on,at, through 情态动词的用法，例如: can,must, may 并列句，例如: A few have long arms, and others have frills. 定语从句，例如: Lots of seaweeds have anchors that hold them in place. 特殊疑问句，例如: Who lives here?