阅读下面材料，在空白处填入适当的内容（1个单词）或括号内单词的正确形式。
If you go out to the fields at night in spring or summer, you can hear frogs singing____(joy) here and there. It seems as if they were performing a field symphony（交响乐）.
The frog is a good and useful creature that benefits human beings. They can catch fast-moving insects. Each frog eats a large number of pests that are ____(harm) to crops. This little creature is regarded ____“the natural enemy of pests”.
____ now frogs are getting fewer and fewer. This is____they are killed and put on the table as a delicious dish by their chief enemy, human beings. It is a shameless and cruel act, isn't it? Another reason responsible for the rapid reduction of frogs is ____farmers use insecticides (杀虫剂) to kill pests and frogs get ____(kill)as a result of drinking poisoned water or eating poison-killed insects.
Something must be done without delay ____(save) frogs. If we don't punish those ____sell and kill frogs to make money, then one day all of us ____(punish) by nature for failing to keep the balance of nature.
