[ Tenses ]
While they (study), the lights went out.
A. While they were studied, the lights went out.
B. While they were studying, the lights went out.

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Simple present/ past/ future tenseVerbs + Infinitives / GerundsPresent TensesIntermediate GrammarTransitional WordsFuture - be going toPast Continues TenseParts of Speech and GrammarMust or Mus notPast Simple vs Present SimpleOther quiz:
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The percentage of gainers on the New York Stock Exchange ______ greater this week than last.
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