根据句意及汉语提示写出单词。
A ______ (鲨鱼)is a dangerous animal.
Many _______ (法律) have been made to protect endangered animals.
The sea animals are all important to the ocean's _______ (生态系统).
Tigers are at the top of the food _______ (链条) in the grassland ecosystem.
Do you know the _______ (优点) of bike riding?