Ordinary body temperature is approximately 37 on the ____ scale.

Ordinary body temperature is commonly understood to be around 37 degrees Celsius, which is also known as the Centigrade scale. This scale is used widely in most countries for everyday temperature measurements, including human body temperature. The Celsius scale is based on the freezing point of water (0 degrees Celsius) and the boiling point of water (100 degrees Celsius) at standard atmospheric pressure.

In contrast, the Fahrenheit scale, which is primarily used in the United States, sets the average human body temperature at approximately 98.6 degrees Fahrenheit. The Kelvin scale, used mainly in scientific contexts, translates temperature into absolute terms, where 0 Kelvin is absolute zero, making the normal body temperature around 310 Kelvin. The Rankine scale, similar to Kelvin but using the Fahrenheit degree increments, is also not standard for reporting body temperature.

Thus, the correct answer is C, as 37 degrees is a specific reference point on the Centigrade scale for normal human body temperature.