The combining form "electr(o)" means?

• A. Running
• B. Pain
• C. Electricity
• D. Swelling

Answer: (C)

The combining form electr(o) denotes electricity, especially electrical activity in the body. The small interfix “o” is just a connective vowel used to join the root to other word parts. You’ll see it in terms like electrocardiography or electroencephalography, which describe recording the heart’s or brain’s electrical activity. That’s why this form means electricity. The other options don’t fit because they relate to movement, pain, or swelling, which use different roots (for example, running would tie to a root about movement, pain to a root like -algia, swelling to edema).