Question

what do red blood cells do?
regulate blood pressure
help the liver filter toxins from the blood
transport nutrients to the bodys tissues
produce insulin
carry oxygen to the bodys tissues.

Explanation:

Red blood cells contain hemoglobin, which binds to oxygen in the lungs and releases it in the body's tissues. This is their primary function. The other options are incorrect: regulating blood pressure is not a direct role of red blood cells; the liver filters toxins on its own (not with red blood cells' help in the way described); nutrients are transported by blood plasma and other components more directly related to that task; insulin is produced by the pancreas.

Answer:

Carry oxygen to the body's tissues.