用括号中所给动词的适当形式填空，使短文完整。

    Alice and her sister want to make the Earth a better place for people. They did a lot of things.

    One day, while they  (walk) in their hometown, they saw hundreds of cigarette butts (烟头) on the ground. The cigarette butts made the town  (look) so ugly that they decided to start a group. They wanted to make people stop  (drop) butts. The group  (call) "No Butts About It" Many people  (start) to join their group after they heard of their stories.

    At the moment, they  (try) to get cigarette companies to put an ashtray (烟灰缸) in each pack of cigarette. Today there are also other "No butts About It" groups in America.