①鉴别二氧化锰和炭粉时，可分别加入氯酸钾后共热，看氧气产生的快慢

②鉴别氧化铜和四氧化三铁时，可分别加入盐酸后微热，看溶液的颜色

③鉴别五氧化二磷和二氧化硅时，可分别加入蒸馏水并搅拌，看固体是否溶解

④鉴别稀盐酸和稀硫酸时，可分别加入硝酸银溶液，看是否有白色沉淀生成

《朝花夕拾》中，起初鲁迅认为范爱农是怎样一个人？

如表是对四种生物结构特征的对比（表中“√”表示有，“×”表示无），其中对哪种生物特征的描述是完全正确的（　　）

根据上下文理解，选择所给词的适当形式填空。

   Yesterday was Sunday. We had no____ . I wrote a letter to my pen pal and____ lunch for my parents. After lunch I took a ____with Mike through the park behind my house. We saw a little girl____ for something. She lost her keys. “She ____  help,” Mike said. So we helped the girl look for her____ . About ten____  later, Mike found them in the grass. The girl was ____ . We spent much time in looking for the____ keys, but we____  very happy because we did a good deed（做好事）.

____