Which of the following true statements, if added here, would best serve as a further explanation of the idea presented in the preceding sentence?
A. Since most heavy materials are too bulky for easy movement.
B. As it takes a great deal of study and research to develop these types of synthetic materials.
C. Since this type of material is never inexpensive to develop or produce.
D. As most military personnel and police officers cannot afford to purchase their own equipment.