The correct answer is: C. All of the above.
A parallel register is a type of register that can store a multiple bit binary number. It is made up of a number of R-S flip-flops, which are used to store the individual bits of the number. The register can be read or written to in parallel, which means that all of the bits can be accessed at the same time.
Option A is correct because a parallel register can store a multiple bit binary number. Option B is correct because a parallel register uses R-S flip-flops. Option C is the correct answer because it includes both Option A and Option B. Option D is incorrect because a parallel register is not erased after a word is read from it. Option E is incorrect because a parallel register is a type of register that can store a multiple bit binary number.