Hot air is heavier than cold air. 

Match the following:

Fill in the blank by using the correct word from the given list:
(litre, second, temperature, thin)

_____ tells us how hot or cold a thing is.

Animals and plants do not need air to breathe.

Define breathing. Name the breathing organ of mammals.

Choose the right words from the given options:

Insects such as the earthworm breathe through their _____. (skin / gills / lungs)