Which of these best describes the tiny leg bones that some whales have, which do not aid in their movement or serve any other function? O structures that grow and improve in function as they are used
O structures that function at certain times of the year or under certain conditions
O structures that will become adaptations when the environment changes
O structures that have lost all or most of their function over evolutionary time

D. structures that have lost all or most of their function over evolutionary time

Explanation:

the question states that the leg bones are almost entirely unused because of evolution

hormones in blood stream

image: dtc.ucsf.edu

endocrine glands secrete hormones into the blood stream near them; the hormones then travel in our bloodstream until it reaches its destination, called a target cell, in distance parts of the body. in the target tissue, hormones lock onto the target’s plasma membrane, called the receptor site.

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation: