Final answer:
To identify all cardiac bypass surgeries, a researcher should use the Cardiac surgery registry, which is tailored for tracking and researching cardiovascular surgical procedures.
Step-by-step explanation:
The researcher wanting to identify all cardiac bypass surgeries performed for a given time period should use the D. Cardiac surgery registry. This specialized registry contains information about patients who have undergone cardiac surgeries such as bypass operations.
It's designed to help healthcare providers and researchers track patient outcomes, evaluate the effectiveness of procedures, and conduct research on cardiovascular diseases and treatments.