16Hit1600
Standard English ConventionsVery hardSubject-verb agreement in relative clauses ('one of the ... that')

Standard English Conventions practice question

Corundum, the mineral that forms both rubies and sapphires, is one of the few naturally occurring substances that ____ hard enough to scratch hardened steel, a property that has long made corundum valuable as an industrial abrasive.

Which choice completes the text so that it conforms to the conventions of Standard English?

  1. A. is
  2. B. were
  3. C. areCorrect
  4. D. being

Answer: C. are

The relative pronoun 'that' refers to the plural noun 'substances,' not to 'one': the sentence identifies corundum as a member of a group of substances that share the property of being hard enough to scratch steel. The plural present-tense verb 'are' agrees with 'substances' and matches the main verb 'is' in time frame. (A) 'is' encodes the classic error of attaching the relative clause to 'one' instead of to the plural noun in the of-phrase. (B) 'were' correctly takes a plural form but shifts to the past tense, contradicting the present-tense frame established by 'is' and 'has made.' (D) 'being' is a nonfinite participle, so the relative clause is left with no finite verb at all.

Why the other answers are wrong

A. is
You attached the relative clause to 'one' instead of to 'substances' — the sentence says corundum belongs to a group of substances that are hard enough to scratch steel, so the verb must be plural.
B. were
You got the plural agreement right, but 'were' shifts to the past tense, which conflicts with the present-tense 'is' and 'has made' elsewhere in the sentence.
D. being
'Being' is a participle, not a finite verb, so the clause beginning with 'that' is left with no working verb at all.

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