Regarding the Gross Primary Productivity $(GPP)$ and Net Primary Productivity $(NPP)$ of an ecosystem,which of the following statements is correct?

• A
  Gross Primary Productivity is always less than Net Primary Productivity.
• B
  Gross Primary Productivity is always greater than Net Primary Productivity.
• C
  Gross Primary Productivity and Net Primary Productivity are the same.
• D
  There is no relationship between Gross Primary Productivity and Net Primary Productivity.