Concept: This question tests the understanding of the multifaceted functions of leaf veins beyond just transport.

Why (B) is correct: The veins of a leaf contain vascular tissues (xylem and phloem) for transport, but they also consist of sclerenchymatous and collenchymatous tissues, which are strong and rigid. These tissues provide mechanical support and rigidity to the leaf blade, preventing it from wilting or tearing easily, especially in windy conditions.

Why other options are wrong:

• (A) Determine the extent of incision of the lamina: The genetic makeup of the plant determines the leaf shape and incision, not solely the veins.
• (C) Hold the leaf blade to light: The petiole and stem hold the leaf blade to light; veins are internal structures providing support within the blade.
• (D) Flutter the leaf in wind thus, helping in cooling of leaf and bringing fresh air: While fluttering can aid cooling and gas exchange, it's primarily the petiole's flexibility and the overall leaf structure that allow fluttering, not the veins' primary function. The veins' role is structural support, which indirectly allows the leaf to withstand wind.

NEET Tip: Remember that plant structures often have multiple functions. For veins, think 'transport AND support'.

Correct Answer: (B)