In the following question, a sentence is given with a part in bold. The given phrase in bold may contain an error. The options following can replace the incorrect phrase. The correct phrase that is to be replaced will be your answer. If the sentence is correct as it is, then select ‘No improvement required’ as the answer.

Despite numerous attempts, the problem remained so unsolvable as it was before.

The correct option is as unsolvable as it was before.

Step-by-Step Explanation:

1. Analyze the original phrase: The given sentence uses the construction "so unsolvable as it was before". In standard English grammar, when showing equality or making a direct comparison of degree, the correct correlative conjunction structure is "as + adjective + as", not "so + adjective + as" (which is typically reserved for negative comparisons like "not so... as").

2. Evaluate the options:

- "as unsolvable as it was before": Correctly uses the pattern as + adjective (unsolvable) + as to compare the current state of the problem to its previous state. The singular pronoun "it" correctly refers back to "the problem", and the past tense verb "was" is grammatically sound.

- "as unsolvable than it was before": Incorrect, because "than" is used for comparative degrees (e.g., "more unsolvable than"), not with "as".

- "as unsolvable as it were before": Incorrect, because "the problem" (it) is singular, so it takes the singular verb "was", not the plural/subjunctive "were".

- "as unsolvable that it was before": Incorrect, because "as... that" is an ungrammatical combination for comparison.

- "No improvement required": Incorrect, since the original sentence contains a grammatical error.

3. Corrected Sentence:
"Despite numerous attempts, the problem remained as unsolvable as it was before."