Science P6 NHPS 2018 SA1 Q02

The table below shows the function of some of the body systems.
Body SystemFunction
AOne part of this system is the longest so the substances take the longest time to pass through it to be broken down.
BOne part of this system has hairs that prevent dust particles from entering the body.
CEvery part of this system needs to work closely with the muscles to provide movement.
Which body systems could A, B and C represent?