Final answer:
Portable defibrillators were mass marketed and sold to healthcare institutions in high volume in the 1990s, despite various models being available since the 1970s. While various models of defibrillators were available since the 1970s, it was in the 1990s that they became widely distributed in healthcare settings.
Step-by-step explanation:
The correct answer is D. Portable defibrillators. In the 1990s, portable defibrillators were mass marketed and sold to healthcare institutions in high volume. These devices were designed to be used by lay persons and provided verbal instructions for use in the first few minutes of a cardiac attack. While various models of defibrillators were available since the 1970s, it was in the 1990s that they became widely distributed in healthcare settings.