The mattress can be stored in a space as small as shoebox but _____ to a thickness of 5 inches when fully inflated.

  1. Expanded
  2. Expand
  3. Expands
  4. Expansion

I think both 1 and 3 can be the correct answers to this question, but the key says its correct answer is "Expands".

I really wonder why "Expanded" can't be the answer. As far as I know, The word "Expand" can be used as both an intransitive verb and transitive verb.

I think "Expanded" can be an answer If the word is used as an transitive verb in the sentence. Am I right?

  • Grammatically it certainly could be either, because you could interpret the passive voice "can be stored" as coordinated with "can be expanded", as you guessed. However, I'm tempted to prefer "expands" as well, simply because descriptions of this kind of product overwhelmingly use the intransitive "expands". So the question merges grammatical and real-world knowledge. Commented Nov 12, 2017 at 11:15

1 Answer 1


Because the first part of the sentence is not past tense. "Expanded" switches tenses halfway through the sentence. Either of these would be correct:

"The mattress could be stored in a space as small as shoebox but expanded to a thickness...

"The mattress can be stored in a space as small as shoebox but expands to a thickness..."

You answer is technically allowable, but awkward. If this is from a test, questions such as this are generally asking for the best answer, not necessarily which one is theoretically allowable under the rules of grammar.

  • It doesn't switch tenses or involve the past at all. It's just the passive voice. Commented Nov 12, 2017 at 11:17

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