Final answer:
Coarse crackles heard during auscultation are typically interpreted as the presence of fluid in the lungs, suggesting conditions like pneumonia.
Step-by-step explanation:
When a nurse hears coarse crackles that are low-pitched and rumbling while auscultating a client's chest, this is most commonly interpreted as the presence of fluid in the lungs (option c). These sounds can be indicative of conditions such as pneumonia, where inflammation affects the alveoli causing them to become filled with fluid, thereby preventing efficient gas exchange. This interpretation aligns with other signs of pneumonia, such as the presence of a "shadow" in a chest radiograph and the production of greenish sputum, which indicate an infection and accumulation of mucus in the lungs.