Ms. Avari is having trouble lifting the 1000N kettlebell. If Ms. Avari does not have enough force to lift it all the way up 4 flights of stairs to her apartment, she can use a simple machine to help her move the kettlebell up to the 4th floor. She might consider using a simple machine called a _________________ to reach the 4th floor balcony.
a
screw
b
wheel and axle
c
lever
d
pulley
d
pulley