All (1)_______ things must fight to stay alive. They have to feed on something and at the same time avoid being (2)_______. Therefore they have to solve this big problem of staying alive in their own way. The danger of being eaten in the sea is great. Those plants and animals that do survive usually (3)_______ very fast and in great numbers.

(4)_______ sea animals have defensive devices which help them to survive. The jelly fish have (5)_______ tentacles (触角) which are used for attack and defense. Another method of (6)_______ which sea plants and animals use is disguise. They usually have the same (7)_______ as their surroundings.

In order to stay alive， animals need to have good senses. Fishes have sharp eyes. Almost all animals are sensitive to (8)_______. Fishes judge movements in the water by (9)_______ of their lines. Fishes and other sea animals can hear well and many of them can (10)_______ different types of warning sound.