Final answer:
The reason that would exclude someone from donating blood is A. The person has cancer. This can affect the safety and quality of the blood. Other options listed generally do not disqualify a person from donating blood.
Step-by-step explanation:
The correct answer to why someone would be excluded from donating blood is A. The person has cancer. This is because certain types of cancer and treatments for cancer can affect the safety and quality of the donated blood. According to general blood donation eligibility requirements, being female and weighing 145lbs (66kgs) (B), having previously donated blood in the last 12 months (C), being 20 years of age (D), or being male with a hemoglobin level over 135 g/L (E) do not automatically disqualify someone from donating blood. However, the person with cancer could be excluded from donation to protect both the donor's health and the recipient of the blood. It is important to consult with the specific blood donation organization for their particular criteria, as these can vary.