Leaves become modified into spines in :-

Options

(a) Pea
(b) Onion
(c) Silk Cotton
(d) Opuntia

Correct Answer:

Opuntia

Explanation:

In Opuntia, leaves become modified into spines to avoid transpiration so as to save water for desert adaptation. The stems of this plant appear like – leaf, termed as- phylloclades which perform the process of photosynthesis.