As we grow older.
a. we lose some of our ability to hear both soft and loud sounds
b. our ability to hear both soft and loud sounds remains stable
c. we lose some of our ability to hear soft sounds
d. we lose some of our ability to hear loud sounds

C. We lose some of our ability to hear soft sounds

Explanation:

As a person grows and matures his/her body requires more amounts of energy to maintain or sustain long enough. As the population grows old or ages what is called in the demographics as population aging, which is a fundamental phenomenon of how one sense slowly stops to respond to external stimulus. Ability to hearing smelling tasting and touching all fade away with tie as man is not immortal neither his senses are, some people who have strong genetic makeup are considered superior to others while the rest of the population goes through the same phases of old age. While some may tend to ignore others. Age is also considered to be a mental rather than a physical aspect.

They carry out the exchange of gases as we breathe ( oxygen and carbon dioxide).

Combustion is the act or process of burning. therefore, i believe the answer is  a: burning wood.