To investigate the conditions for rusting, following experiment was performed.
In which test tube, nails rusted most heavily and what inference can be drawn from it?
(A) Test tube P, water is needed for rusting.
(B) Test tube Q, air is needed for rusting.
(C) Test tube R, boiled water increases the rusting speed.
(D) Test tube S, presence of sodium chloride increases the rusting speed.