Which statement is BEST supported by research?

a$.$

The training environment should mimic the on$-$the$-$job environment as much as possible.

b$.$

Supervisors should not discuss training with their subordinates.

c$.$

Trainees are more likely to transfer new skills when they have heavy workloads.

d$.$

Trainees should learn in an environment very different from the one in which they will need to use their skills so they feel challenged.