Check each option against the two conditions in the question, equal availability and difficulty of control. Money differs by income, human energy differs by health and age, and equipment differs by what a household owns, so none of these three is equally available to everyone. Time is the one resource every person receives in the same fixed amount each day, so it satisfies equal availability, and because it constantly runs out and cannot be stockpiled, it is genuinely hard to manage even though the idea of time itself is simple. \[\boxed{\text{Time}}\]