Select the option that can correctly replace the underlined phrase in the sentence. If the sentence is already correct, select 'No improvement required'.

The architect ensured that the blueprints were drawn in accordance to the guidelines set by the urban planning committee.

The correct option is in accordance with the guidelines.

Step-by-Step Explanation:

1. Understanding the Idiomatic Expression:
In English grammar, fixed prepositional phrases require specific prepositions to be grammatically correct. The standard idiomatic phrase is "in accordance with", which means in agreement with, conforming to, or following a set of rules, laws, or instructions.

2. Analyzing the Given Sentence:
The original sentence contains the underlined phrase "in accordance to the guidelines". Using the preposition "to" after "accordance" is grammatically incorrect in standard English usage.

3. Evaluating the Options:
• "in accordance of the guidelines": Incorrect preposition; "of" cannot be paired with "in accordance".
• "in accordance upon the guidelines": Incorrect preposition; "upon" is contextually wrong.
• "No improvement required": Incorrect, because the original sentence contains a prepositional error.
• "in accordance with the guidelines": Correct, as it properly uses the preposition "with".

Conclusion:
Replacing the underlined phrase gives the grammatically correct sentence:
"The architect ensured that the blueprints were drawn in accordance with the guidelines set by the urban planning committee."