96J6 A
 To ensure effective HF communications, GMDSS operators should:
A. Employ the short rules of propagation selection or rely on previous successful communications as a guide.
B. Disregard the short rules of propagation selection and try different bands until one works.
C. Do not rely on previous successful communications on the selected frequency band - the ionosphere changes too rapidly and inconsistently.
D. Rely on the equipment calculations of Optimum Usable Frequency.
