BOD values (in ppm) for clean water \( (A) \) and polluted water \( (B) \) are expected respectively as:
\( A > 25, \; B < 17 \)
\( A > 50, \; B < 27 \)
\( A > 15, \; B > 47 \)
\( A < 5, \; B > 17 \)