The system that deals with breathing is known as the

The system that helps to produce young ones is the 

A group of organs that work together to perform a particular task is called a/an

Two or more bones are connected at

Which of these is a man-made source of light?

Which of these always travels in a straight line?

Which of these is a pleasant sound?

You apply force to

The main source of light on the earth is

An object  does not cast a shadow. It is most likely made up of X material. X could be