Which of the following are radiation-shielding design considerations?

1. The mean energy of the x-rays that will strike the barrier
2. Whether the barrier is of a primary or secondary nature
3. The workload of the unit
4. The use factor of the unit
5. The occupancy factor behind the barrier

a. 1, 2, 3, and 4 only
b. 1, 3, 4, and 5 only
c. 2, 3, 4, and 5 only
d. 1, 2, 3, 4, and 5

d. 1, 2, 3, 4, and 5