The keyboard, mouse, display, and system units are:​

input devices?

Explanation:

Keyboard: It is used to give input through typing of the keys in keyboard. Mouse: It is used to give input through clicking mouse or selecting the options. System unit: It collectively defines the motherboard and CPU of the computer.

they are hardware components of a computer

do not use any of these common illegal characters/symbols:

# pound

% percent

& ampersand

{ left curly bracket

} right curly bracket

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< left angle bracket

> right angle bracket

* asterisk

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$ dollar sign

! exclamation point

' single quotes

" double quotes

: colon

@ at sign