The Atmospheric Layer Containing 75% of the Mass of Earth's

question 22

Multiple Choice

The atmospheric layer containing 75% of the mass of earth's air is the ____.

• A) thermosphere
• B) mesosphere
• C) stratosphere
• D) troposphere
• E) tropopause

---

Definitions:

Myelination

The process of coating the axons of neurons with a fatty layer called myelin, which speeds up the transmission of neural signals.

Cerebellum

A region of the brain that plays a key role in motor control, coordination, precision, and accurate timing of movements, also involved in some cognitive functions.

Fetus

A developing mammal or human from the end of the embryonic period (in humans, approximately 8 weeks after conception) until birth.

Motor Development

The progression of muscular coordination and the ability of the body to move and manipulate objects, which occurs in stages from simple reflexes to complex movements.