Final answer:
After a fall, a pregnant soldier should be advised to stay still to assess for injuries and to seek medical attention if there are concerns. Continuing to exercise is not recommended.
Step-by-step explanation:
The correct action for a soldier who is less than 20 weeks pregnant and falls while doing step aerobics is b) Advise her to stay still and assess for injuries and c) Recommend seeking medical attention if there are concerns. What should NOT be done is d) Instruct her to continue exercising to avoid stiffness. After a fall, it is crucial to ensure that there are no injuries that could be aggravated by further movement, and exercising could potentially cause more harm to both the soldier and the pregnancy. Seeking medical attention is crucial if there are any concerns about the well-being of the mother or the fetus.