What types of tests are included in bioassays?

The inclusion of urinalysis and external monitoring of the thyroid in bioassays is correct because bioassays are specifically designed to measure the presence and concentration of substances in biological samples that can provide information about an individual's exposure to certain types of radiation or radioactive materials.

Urinalysis can reveal metabolites or isotopes excreted by the body after exposure to radiological substances, allowing for monitoring of internal contamination. Similarly, external monitoring of the thyroid is crucial since the thyroid gland can uptake radioactive iodine, and monitoring its levels can give insights into the degree of exposure to radioactive materials. These methods are directly related to the assessment of biological responses and dosimetry in the context of radiation safety.

In contrast, other options involve tests that do not primarily serve the bioassay purpose. Blood tests and MRI scans, for example, are used for various medical diagnostics but are not specifically tailored for assessing radiation exposure. X-rays and physical examinations also fall into standard medical practices rather than bioassays. Genetic testing and biopsies, while they can be relevant in certain contexts, do not inherently assess radiation exposure or biological responses to radioactive materials in the same manner as the correct choice does. Therefore, the focus on urinalysis and external monitoring makes option B