1．Falling objects are pulled down to the ground by .
A．gravity B．resistance C．speed D．acceleration（加速度）
2．Why do people make parachutes(降落伞)?
A．To look pretty and colourful in the air. B．To slow down the falling speed.
C．To push against the air in the sky. D．To accelerate the falling movement.
3．Which did Galileo discover?
A．A heavy ball falls faster than a light ball. B．A light ball falls faster than a heavy ball.
C．A light ball and a heavy ball fall at the same speed.
D．A light ball and a heavy ball fall at different speed.
4．Which of the following is NOT true according to the passage?
A．Heavy and light objects fall equally when they are different in size.
B．When air resistance equals gravity, objects fall at terminal speed.
C．Without air; all falling objects get faster and faster at the same rate.
D．Slippers（拖鞋） and boots （靴子）fall at the same speed because they have the same shape
