The service engineer of the "Tunnel Ventilation" company (page80) has reported the following."A diagnosis in our ventilation system has shown,that if any of the three smoke detectors delivers a signal,fan1 is always running.Since we have installed speed control system in our DC motors,we have to change the motor brushes very often.When one fan needs to run,the operation of a different fan each time should spread the wear of the brushes evenly over the three fans.The company decided to bid for a new software.

WHAT IS THE .....

A. statement list

B. Ladder diagram

C. flowchart of the system