The correct answer is: A. Both A and R are true and R is the correct explanation of A.
Live loads are loads that are not permanent, such as the weight of people, furniture, and equipment. Dead loads are loads that are permanent, such as the weight of the structure itself and any attached objects.
Live loads are more uncertain than dead loads because they can vary depending on the use of the structure. For example, a building that is used as an office will have a different live load than a building that is used as a warehouse.
The load factor is a factor that is used to calculate the design load for a structure. The design load is the load that the structure must be able to support without failing. The load factor for live load is greater than that for dead load because live loads are more uncertain.
Therefore, both A and R are true and R is the correct explanation of A.