Dolphins are know as cetaceans, or

Dolphins are know as cetaceans, or marine (1)_______they breathe air, they are warm- blooded, and they bear live young ones called (2)___
The size of dolphins vary greatly. The smallest Dolphin is just about 50 kg weight and 1.2 meters in length (3)____ the largest one can weigh up to 8.200kg and is 10 meters long.
Dolphins are sociable creatures. They swim together in group known as (4)_. They show great ability in the water and you can often (5) ____ them playing (6)__ ships. Dolphins are interested in humans and often rescue people in the sea (7) _ are in danger.
They are intelligent creatures and make sounds to (8)_­____ with each other. Scientists have studied Dolphins (9)_____ many years and now looking into the possibility of Dolphins (10) __ able to carry out tasks under the sea.