All your cells contain proto-oncogenes, which can change into cancer-causing genes. why do cells possess such potential time bombs?
a. cells produce proto-oncogenes as a by-product of mitosis.
b. proto-oncogenes are necessary for the normal control of cell growth and division.
c. proto-oncogenes protect cells from infection by cancer-causing viruses.
d. proto-oncogenes are unavoidable environmental carcinogens.
e. proto-oncogenes are genetic junk that has not yet been eliminated by natural selection.

B

Explanation:

Proto-oncogenes contain proteins that stimulate cell division, inhibit cell differentiation,and prevent cells from dying. These processes are important for normal development and for the maintenance of tissues and organs.

An alternation of these proto-oncogenes leads to the formation of oncogenes which are particularly responsible for abnormal cell division resulting in cancer cells

the device is called “ rocket engine”

answer;

d. are made mostly of liquid

explanation;

-the general   composition and structure planets includes; they have a thick gas and liquid layer covering a small,solid core. mostly the gases are hydrogen and helium atmosphere and layers of liquid hydrogen. for instance neptune and uranus are examples of the outer planets, they have a core covered by ice and ammonia.

-neptune's atmosphere is hydrogen and helium with a bit of methane so there is no oxygen to breath and the interior is made up of frozen water and ammonia with a rock and iron core. thus, there is no liquid water or solid surface to survive.