A part of de-starched leaf of a potted plant was covered with black paper strips on both sides and the plant was kept in sunlight for 8 hours. The leaf was then tested with iodine after boiling it in alcohol. Only the uncovered part of the leaf turned blue black. The inference is that:

(a) CO₂ is necessary for photosyrrthesis.

(b) Light is necessary for photosynthesis.

(c) Chlorophyll is necessary for photosyrthesis

(d) Water is necessary for photosymthesis.