Select the word segment that substitutes (replaces) the bracketed word segment correctly and completes the sentence meaningfully.
The better-known combat units in (where abroad nationals served in another country's army force) are the Gurkha regiments of the British Army and the Indian Army, and the French Foreign Legion.

Correct option is B

The correct replacement is option (b).

Explanation:

• The sentence requires a correct relative clause describing “combat units”. The appropriate relative pronoun here is which, not where.
• The phrase abroad nationals is incorrect. The standard term is foreign nationals.
• The correct collective term is armed forces, not “army force”.
• Option (b) is grammatically complete and meaningful: it clearly explains that foreign nationals serve in another country’s armed forces.

Why other options are incorrect:

• (a): Contains incorrect word forms (nationales) and an awkward structure.
• (c): Contains incorrect spelling (nationales) and is grammatically faulty (“which ... serving” needs restructuring).
• (d): Not correct because the bracketed part is clearly wrong.

So the correct answer is (b)