Cactus spines are modified
· branches
· leaves
· stems

Leaves

Explanation:

The spines of a cactus help prevent water loss by reducing air flow close to the cactus and providing some shade, while also deterring most animals that would make a meal of the cactus.

the menstrual cycle – higher tier. negative feedback mechanisms affect the production of hormones in the menstrual cycle. oestrogen also stimulates the release of lh (luteinising hormone) from the pituitary gland, which in turn controls the production of progesterone.