Which One of the Following Statements Concerning Net Working Capital

Which one of the following statements concerning net working capital is correct?

A) Net working capital increases when inventory is purchased with cash.
B) Net working capital must be a positive value.
C) Total assets must increase if net working capital increases.
D) A decrease in the cash balance also decreases net working capital.
E) Net working capital is the amount of cash a firm currently has available for spending.