Over time, the star-gas-star cycle leads the gas in the Milky Way to .

a) have a lower abundance of heavy elements
b) have a greater abundance of heavy elements
c) become denser and hotter
d) become denser and have a greater abundance of heavy elements

b) have a greater abundance of heavy elements

Explanation:

The star-gas-star cycle is the process by which a star changes over the course of time. Once a star like the Sun has exhausted its nuclear fuel, its core collapses into a dense white dwarf

Because young stars are formed from the explosions of other stars, and those stars build up layers over time and have these heavy elements in them. So when they explode, you mainly have  those  heavy elements in molecular clouds for stars to form out of those.

The correct option is;

b) have a greater abundance of heavy elements

Explanation:

The star gas cycle starts refers to the transition from the formation  of hot bubbles of about 1,00000 K and density of 0.01 atom per cm³ to warm atomic hydrogen clouds to cool atomic clouds of density 100 atoms per cm³   unto molecular clouds  of density 300 atoms per cm³ after which molecular star forming cloud cores are formed which have densities of 10000 atoms per cm³ then a new star is formed which eventually leads to stellar burning and the formation of heavy elements.

thermal energy is the answer

answer: the metamorphic rocks are formed when they are exposed to high pressure and high temperatures. this happens when one of the earth's plates comes in contact with the other plate by traveling in opposite directions, straight into each other or slipping under one another. the friction that is caused by this activity results in   melting of rocks and when it cools they are known as metamorphic rocks. this process needs a controlled amount of pressure and temperature otherwise it may turn into magma.