After its main sequence existence, a medium-sized star, like our sun, will become a
a. protostar
b. red dwarf
c. white dwarf
d. red giant
e. red supergiant

The answer is D. The life cycle of a star is dependent on its mass. Stars by forming at nebulas as protostars. When the sun exhausts hydrogen fuel at its core, the core begins to fuse helium to carbon and the core becomes hotter but smaller. The outer layers are pushed outwards and the sun becomes larger and paler. Later, the helium fuel begins to run out and the sun loses the outer expanding layers into a planetary nebula. The remaining core is a white dwarf.

Stars that are 10 times our sun's solar mass just explode to supernovas when their hydrogen fuel is exhausted.

answer; i believe the correct answer is ( proteins );

both anaerobic and aerobic respiration use glucose (or other carbohydrates), proteins and lipids to produce atp and nadh. cell uses those energy molecules, obtained from food and   breaks them down during the chemical reactions of respiration. in anaerobic respiration, nadh is regenerated to nad+ by enzymes lactate dehydrogenase (lactate is produced, e.g. in muscle cells) or by alcohol dehydrogenase where ethanol is produced (alcohol fermentation), while in aerobic respiration, electrons from nadh are deposited in the mitochondria to regenerate nad+ (electron transport chain. anaerobic respiration produces 2 atp per molecule of glucose compared to aerobic respiration where about 38 atp molecules are produced.