Cuba's electrical grid collapses, leaving the island without power according to state-run company. What infrastructure failed?

The correct answer is the electrical grid because the question specifically states that Cuba's electrical grid collapsed, resulting in the entire island being left without power. When an electrical grid fails, it typically means that the system responsible for generating, transmitting, and distributing electricity is compromised, leading to widespread power outages. This infrastructure is crucial for everyday functions, including residential power needs, essential services, and various forms of technology.

The other infrastructure options—water supply, transportation system, and healthcare system—are not relevant to the specific event described, as they do not pertain to electricity supply. While a failure in the electrical grid could indirectly affect the operation of these systems (such as water supply and healthcare services), the specific failure identified in the context of the question is clearly the electrical grid itself.