What hormone that occurs in both plants and animals is responsible for operating stomatal closure in plants and regulating blood vessel diameter in mammals?

A) hydrogen peroxide
B) nitric oxide
C) salicylic acid
D) cytokinin
E) progesterone

Nitric oxide is a hormone that functions in both plants and animals. In plants, it is responsible for operating stomatal closure, which helps conserve water during drought conditions. In animals, it regulates blood vessel diameter, which affects blood pressure and circulation. Hydrogen peroxide and salicylic acid are plant hormones, while cytokinin and progesterone are animal hormones and do not play a role in controlling stomatal closure in plants.