Step 1: Time is unique among resources because every person gets the same 24 hours a day, regardless of income or status, so it is available equally to all.
Step 2: It is easy to understand as a concept, but it cannot be saved, stored or increased, so managing it well is genuinely hard.
Step 3: Money, human energy and equipment all vary from family to family and person to person, so they are not equally available to everyone.
Step 4: The correct answer is option 4, Time.