Resons for rejection
A. Becuase SOME duties have no human health impact, cannot mean licence should not be required at all
C. The HA make decisions that AFFECT the health of people. Doesn't necessarily mean their decisions can THREATEN their health. For ex, an admin might be assigned a role of maintaining gloves and other usables in hospital. If those are not present, may affect the lives but not necessarily threaten.
D. Substances CAN POSE A THREAT, means don't necessarily pose a definitive threat to the human lives.
E. IMO, because the option is talking specifically about a subset of artists who do not maintain sanitation, this faulty group should not be taken as a sample size for the 'performance of tasks normally carried out' condition of the question. Hence not correct representation of the profession itself.
Why B is correct.
Q - If INCOMPETENCE in performance of tasks NORMALLY CARRIED OUT poses a THREAT to human lives
B - POOR WORK done by interior designers, in NO REALISTIC CIRCUMSTANCES, poses a DANGER to human lives
Though this is a negation option, it is almost verbatim restating the principle.