下列环境中，铁制自行车最容易生锈的是（　　）

阅读下面的诗歌，完成下面题目。
                                                                                                   金陵怀古
                                                                                               〔唐〕刘禹锡
                                                                                      潮满冶城^①渚，日斜征虏亭^②。
                                                                                      蔡洲^③新草绿，幕府^④旧烟青。
                                                                                      兴废由人事，山川空地形。
                                                                                      后庭花一曲，幽怨不堪听。
      ［注释］①冶城：东吴著名的制造兵器之地，在今南京朝天宫一带。②征虏亭：亭名，故址在今南京市玄武湖北。③蔡洲：江中洲名。东晋陶侃、温峤曾起兵在此讨伐叛军。④幕府：山名。东晋丞相王导曾在此建立幕府屯兵驻守。

Cat: Good morning, Mr Tiger.

Tiger: Good morning, Mr Cat. What date is it today? Is it the 3rd of July?

Cat: Yes.

Tiger: Oh, today is my birthday.

Cat: Happy birthday! What would you like as a birthday present? How about a big cake with some candles on it?

Tiger: No, thank you. I'd like one hundred rabbits.

Cat: One hundred rabbits? I'm sorry, Mr Tiger. I haven't got any rabbits for you.

图示是一汽车在行驶过程中通过交叉路口的速度一时间图象．由图象可知（   ）