Select the option that can be used as a one-word substitute for the given group of words. That which cannot be conquered

Correct — D. The gloss is that which cannot be conquered, and that is what invincible literally says: in- (not) + the Latin verb vincere (to conquer).

Every option here is the same negative prefix on a different Latin root, so the prefix decides nothing. Match the verb in the gloss to the root and the item collapses.

An invincible army, argument or champion is one that cannot be beaten → option (d).

Why the others are wrong

• (a)
  Ineffable — Ineffable means too great or too sacred to be put into words, from Latin fari, to speak. It answers cannot be expressed, not cannot be conquered.
• (b)
  Indelible — Indelible is what cannot be rubbed out — an indelible mark, an indelible memory. The root is delere, to blot out, so it fails the conquering test.
• (c)
  Invisible — Invisible is what cannot be seen, from videre, to see. It is the reflex pick whenever a gloss opens that which cannot be, but the verb in this gloss is conquered.

One-word substitution is decided by the root under the prefix, not by which word feels grandest.

All four options are Latin verbs carrying a negative in-: vincere (conquer) gives invincible, videre (see) gives invisible, delere (blot out) gives indelible, fari (speak) gives ineffable.

So read the gloss for its verb, then find the option built on that verb. Where the prefixes are identical, the root is the whole question.

Key facts

• Invincible comes from Latin in- (not) plus vincere (to conquer) — unable to be defeated.
• Indelible traces to Latin delere, to blot out — impossible to remove or forget.
• Ineffable traces to Latin fari, to speak — too great to be put into words.
• Invisible traces to Latin videre, to see — unable to be seen.

Common traps

• Picking invisible because the gloss opens cannot be and the eye stops at the prefix.
• Reading indelible as cannot be defeated by confusing delere with defeat.

No directly related past PYQ was found.