The Amount of Physical Capital Is a ________ Variable;________

The amount of physical capital is a ________ variable;________.

A) flow; its usefulness lasts over a long period of time
B) flow; it is usually put in place and maintained over a long period of time
C) stock; any flow of investment adds to the current capital stock
D) stock; most equipment is solidly built and lasts for a long time
E) stock; it generally increases its value through use