Xerophytic adaptations minimizing evaporation gradient

Steps:

• Water potential gradient between saturated leaf air and dry atmosphere drives transpiration; reducing it conserves water.
• Hairs (1) trap moist air, increasing boundary layer humidity and lowering gradient.
• Sunken stomata (2) lengthen diffusion path through still, humid air, reducing gradient.
• Thick cuticle (3) limits water diffusion through epidermis but does not alter atmospheric humidity gradient.
• Rolled leaves (4) create enclosed humid microenvironment, decreasing external gradient.

Why B is correct:

• B selects 1, 2, and 4, which directly reduce the vapor pressure deficit by enhancing local humidity per Fick's law of diffusion.

Why the others are wrong:

• A includes 3, which blocks water loss but ignores gradient reduction.
• C omits 2, excluding sunken stomata's boundary layer effect.
• D omits 1, excluding hairs' moisture-trapping role.

Final answer: B