Most cells in the body of a fruit fly contain eight chromosomes. In some cells, only four chromosomes are present, a condition
which is a direct result of

it's a direct result of meiotic cell division

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.

the real answer is b. scintillation counter