What is used to measure radiation exposure to the body?

The correct choice highlights the units rem and millirem, which are specifically designed to measure radiation exposure to the human body. These units are crucial in the field of radiological protection, as they quantify the effective dose of ionizing radiation based on its potential biological impact. The rem measures the dose of radiation absorbed by the body, taking into account the type of radiation and its effect on different tissues.

In contrast, the other options mention units that are not applicable to measuring radiation exposure. Wells and joules pertain more to energy and work rather than radiation. Volts and amperes are units used in electrical measurements, focusing on voltage and current, which have no direct relation to radiation exposure. Pascals and bars are units of pressure, not related to the measurement of radiation.

Understanding these distinctions is essential for anyone working in environments where radiation is present, as it underscores the importance of using the correct units for safe handling and exposure assessment.