Concept:The Caps Lock key is a toggle key used to type letters in uppercase without holding Shift.
Explanation:Caps Lock changes the case of letters typed on the keyboard.
When Caps Lock is on, pressing a letter key produces an uppercase letter, for example, "A".
When Caps Lock is off, pressing the same key produces a lowercase letter, for example, "a".
Therefore, it is used to switch between upper and lower case letters.
Answer:C. Switch between upper and lower case letters.