The Most Significant Advancement in the Early Days of Radiography

The most significant advancement in the early days of radiography came in 1913 when W. D. Coolidge:

A) became the first to alert the profession of the dangers of radiation exposure and advocated for the science of radiation protection.
B) exposed a prototype of a dental radiograph, setting the stage for preventive oral health care.
C) developed a variable, high kilovoltage x-ray machine compatible with the paralleling technique.
D) introduced an x-ray tube that allowed for an x-ray output that could be predetermined and accurately controlled.