Correct Option: C. SHIFT, CTRL and ALT keys. Detailed Explanation: Modifier keys are special keys on a computer keyboard that modify the function of other keys when pressed together. They do not produce a character by themselves but change the output of other keys. The most common modifier keys are:

1. SHIFT: This key is used to type capital letters and other alternate "upper" characters on keys. For example, pressing the SHIFT key along with the letter "a" will produce "A". It is also used in combination with other keys to perform various functions, such as selecting text or creating shortcuts.
2. CTRL (Control): This key is used in combination with other keys to perform specific commands. For example, pressing CTRL + C copies selected text, and CTRL + V pastes it. The CTRL key is essential for keyboard shortcuts in many applications.
3. ALT (Alternate): Similar to the CTRL key, the ALT key is used in combination with other keys to access alternate functions. For example, pressing ALT + F4 closes the current window in Windows operating systems. The ALT key can also be used to access menu options in many software applications.

These three keys (SHIFT, CTRL, and ALT) are the primary modifier keys found on most standard keyboards, making option C the correct answer. Why Other Options Are Incorrect:

• Option A: DEL, ESC and ALT keys.
• DEL (Delete): This key is used to delete characters or files but does not modify the function of other keys.
• ESC (Escape): This key is used to cancel operations or close dialogs but is not a modifier key.
• ALT: While this is a modifier key, the presence of DEL and ESC in this option makes it incorrect as they do not serve the purpose of modifying other keys.
• Option B: CTRL, CAPS LOCK and DEL keys.
• CAPS LOCK: This key toggles the capitalization of letters but does not modify the function of other keys in the same way as SHIFT, CTRL, or ALT. It is not considered a modifier key in the same context.
• DEL: As mentioned, this key is for deletion and does not modify other keys.
• Therefore, this option is incorrect because it includes CAPS LOCK and DEL, which are not modifier keys.
• Option D: CTRL, ALT and DEL keys.
• DEL: Again, this key is not a modifier key. While CTRL and ALT are modifier keys, the inclusion of DEL makes this option incorrect.
• This option is often associated with the "CTRL + ALT + DEL" command used in Windows to access the task manager or lock the computer, but it does not change the fact that DEL is not a modifier key.

Revision Summary:

• Modifier keys include SHIFT, CTRL, and ALT, which change the function of other keys.
• DEL and ESC are not modifier keys; they perform specific actions but do not modify other key functions.
• CAPS LOCK toggles capitalization but does not modify other keys like SHIFT does.
• Understanding the role of each key is crucial for effective keyboard usage and shortcuts.