Final answer:
Microwaves can be used for deep heating therapy within the human body to treat muscular pains, spasms, tendonitis, and rheumatoid arthritis.
Step-by-step explanation:
Microwaves are often used for heating within the human body, as they can penetrate deep into tissue. This is called microwave diathermy and is used to treat muscular pains, spasms, tendonitis, and rheumatoid arthritis.
As a form of deep heating therapy, microcurrent can be effective for pain relief, making option b) Pain relief an accurate statement.