Select the word segment that substitutes (replaces) the bracketed word segment correctly and completes the sentence meaningfully.
In Nine men's Morris board game players try to form ‘mills’—(three of there own men lining straightly or erectly)—allowing a player to remove an opponent's man from the game.

Correct option is C

The correct replacement is option (c).

Explanation:

• The phrase there is incorrect here because it indicates place. We need the possessive form their to show ownership (men belonging to the player).
• The words straightly or erectly are unnatural and do not convey the standard description of a line on a board. In board games, a straight line is described as horizontal or vertical.
• Also, the structure should be parallel and meaningful: lined horizontally or vertically correctly explains how three men form a “mill”.

Corrected segment:

• three of their own men lined horizontally or vertically

Why other options are incorrect:

• (a): Although their is correct, lining straightly or erectly is incorrect and unidiomatic.
• (b): Uses there (wrong possessive) and also mixes incorrect/awkward wording.
• (d): Not correct because the bracketed part contains clear errors.

So the correct answer is (c)