The archaeological discovery was ______ significant that international research teams immediately requested permission to excavate the site.

Answer and explanation

Correct answer: C. so

  1. Step 1: Recognize correlative result clause: The adjective 'significant' is followed by a 'that...' clause expressing consequence.
  2. Step 2: Modifying an adjective followed by 'that' requires the adverb 'so' ('so [adjective] that...').
Answer
so.
Why not the others: 'too' pairs with infinitive 'to' ('too significant to ignore'); 'very' cannot introduce a 'that' result clause; 'such' modifies a noun phrase ('such a significant discovery that...').

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