The correct answer is D. data naturally needs to flow in and out in serial form.
Serial access memories are useful in applications where data naturally needs to flow in and out in serial form. This is because serial access memories can only access data one bit at a time, which makes them slower than random access memories (RAMs). However, serial access memories are often used in applications where speed is not as important as cost or power consumption.
For example, serial access memories are often used in embedded systems, such as those found in cars and appliances. These systems often need to store a large amount of data, but they do not need to access that data very quickly. Serial access memories are also used in some types of memory cards, such as CompactFlash cards.
Option A is incorrect because serial access memories can store any type of data, not just numbers. Option B is incorrect because serial access memories can have long access times, depending on the specific type of memory. Option C is incorrect because each stored word is processed the same way in a serial access memory. Option E is incorrect because serial access memories are useful in some applications.