Beginning in one's twenties, the protective cartilage in the joints can show signs of deterioration, such as thinning and becoming cracked and frayed. If these changes become pronounced they can lead to ____

The ________ is usually inactive, especially during sleep, but it emits bursts of impulses in response to meaningful events

Fill in the blank(s) with the appropriate word(s).

Ebony has an excessive, unrealistic fear of heights. Her phobia is called ______

a. claustrophobia c. acrophobia b. hydrophobia d. agoraphobia