Answer:
a. training
Step-by-step explanation:
"Training" is crucial when it comes to new workers or workers who are coming back after a long vacation or whatever reason. The risk of injuries and making mistakes is high for new workers because they are still adjusting to the company's processes. This is similar to a baby who's learning to walk. The baby makes several slips before mastering the skill. For a worker who has been away from the workforce, training should also be given because that worker needs to freshen up his skills and relearn what he needs to grasp before working.
This situation is especially true to construction workers who work under contractual projects. This means, they always have to be trained every time about their new jobsite before even working.