In MS-DOS display configuration, which MODE command sets a color display adapter to 40-column text mode with color enabled?

Introduction / Context:
Early DOS systems allowed users to change the text mode characteristics of the display adapter from the command line. Color adapters could be configured for 40 or 80 columns, which influenced readability on televisions and early monitors. Knowing the precise syntax of the MODE command is essential for correctly setting the screen layout.

Given Data / Assumptions:

• You are using a color display adapter compatible with DOS MODE settings.
• You specifically want a 40-column text layout (wider characters, fewer columns).
• You also want color output active.

Concept / Approach:
The MODE utility accepts parameters that select display width and color capabilities. The token "CO" denotes a color mode, and the numeric suffix indicates the column count. Thus, "MODE CO40" sets the adapter to a 40-column color configuration. Other strings such as "MODE COLOUR" or symbolic verbs like "MODE CHANGE" are not valid DOS syntax for this purpose, and switches like "/C" are unrelated to text-width configuration in classic DOS.

Step-by-Step Solution:

Verification / Alternative check:
Run MODE without arguments to display current settings, then toggle to MODE CO40 and again to MODE CO80 to confirm that the width and color settings are changing as expected.

Why Other Options Are Wrong:

• MODE COLOUR: Not a recognized DOS parameter.
• MODE/C: Not the syntax for setting text columns and color.
• MODE CHANGE: Not a DOS command.
• None of the above: Incorrect because MODE CO40 is valid and correct.

Common Pitfalls:
Assuming every DOS version supports identical MODE arguments, ignoring that some shells echo minimal feedback after a mode change, and confusing color enablement with palette control, which is separate.

Final Answer:
MODE CO40