Fill in the blank with the correctly spelt word. The species showed remarkable __________ to extreme conditions.

Correct — B. The blank needs a noun: the species showed remarkable [something] to extreme conditions.

Build it from the adjective adaptable, which ends in -able. An -able adjective makes its noun in -ability: capable → capability, reliable → reliability.

So adaptable → adaptability: -ability with an a, and the -ity ending with one t → option (b).

Why the others are wrong

• (a)
  adaptibility — adaptibility borrows the -ibility of -ible adjectives, as in flexible → flexibility. The adjective here is adaptable, spelt with an a, so its noun is -ability.
• (c)
  adaptibilitye — adaptibilitye has two faults: the -ibility of -ible words, and a stray final e. Nouns in -ity end in y, as in ability and stability.
• (d)
  adaptabilitty — adaptabilitty gets -ability right but doubles the t of the suffix. The noun ending -ity has a single t: ability, stability, capability.

A spelling cloze uses the sentence to fix the part of speech, then tests the letters. Here 'remarkable __________ to extreme conditions' needs a noun.

That noun comes from an adjective you already know, adaptable. Adjectives in -able form nouns in -ability, and adjectives in -ible form nouns in -ibility: possible → possibility.

So the real question is adaptable or adaptible. The dictionary form is adaptable, and the noun follows it.

Key facts

• Adaptable (adjective) → adaptability (noun).
• -able adjectives form nouns in -ability: capable → capability, reliable → reliability.
• -ible adjectives form nouns in -ibility: flexible → flexibility, visible → visibility.
• The noun suffix -ity has a single t and ends in y: ability, stability.

Common traps

• Writing -ibility because flexibility and visibility look similar. Those nouns come from -ible adjectives, and adaptable is -able.
• Doubling the t of -ity after seeing the t in adapt. The suffix is -ity, with one t.

No directly related past PYQ was found.