Final answer:
Clients taking Omeprazole should report to their Health Care Provider if they experience black, tarry stools, diarrhea, or abdominal pain, as they can be signs of serious conditions such as gastrointestinal bleeding or adverse reactions to the medication.
Step-by-step explanation:
Clients taking Omeprazole should report all of the following symptoms to their Health Care Provider: A. Black, tarry stools, B. Diarrhea, C. Abdominal pain. These symptoms can be indicative of serious conditions such as gastrointestinal bleeding associated with ulcers, which may present as dark stools. If no treatment is provided, the condition could worsen, potentially leading to stomach perforation -- a severe health emergency. Additionally, chronic diarrhea and abdominal pain could signal adverse reactions or complications from taking Omeprazole that warrant medical attention.