Part A Fundamentals is closed book. It requires you to respond to the question base on the knowledge you have of welding, codes, NDT, welding symbols, etc.

That information is referred to as the "body of knowledge" that you draw upon based on your experience, reading, and training in the industry.

If you study radiography or if you have some working knowledge of radiography or experience looking at exposed RT film you will recollect that a tungsten inclusion represents something that is more dense than the carbon steel, aluminum, etc. and would allow less radiation to pass through. The less radiation that passes through the test piece, the lighter the image. In contrast, a crack that is parallel to the beam of radiation would represent less thickness (or less density) thereby allowing more radiation to pass through and produce a darker image on the film.

Best regards - Al