Select the most appropriate option that can substitute the underlined segment in the given sentence. If there is no need to substitute it, select ‘No substitution required’.
The authorities are assured the people that they will look into the matter.

To determine the correct substitution for the underlined segment "are assured" in the sentence "The authorities are assured the people that they will look into the matter", let us analyze the sentence structure and verb tenses:

1. Identify the Subject and Voice:
The subject of the sentence is "The authorities". The sentence describes an action performed by the authorities (assuring the people). Therefore, the verb must be in the active voice.
The phrase "are assured" is in the passive voice (present simple passive), which would mean someone else is assuring the authorities. This does not fit the context because the authorities are the ones performing the action of assuring "the people".

2. Determine Subject-Verb Agreement:
The subject "The authorities" is plural. Therefore, we must use a plural verb form ("have") rather than a singular verb form ("has"). This rules out the option "has assured".

3. Select the Correct Tense and Aspect:
To express that the authorities have already performed the action of giving an assurance to the people, we use the present perfect tense in the active voice.
The formula for the present perfect active voice is: Subject + have/has + past participle (V3).
Applying this to our plural subject, we get: "have assured".

4. Evaluate the Options:
- "has assured": Incorrect because "The authorities" is plural, requiring "have".
- "have been assured": Incorrect because it is in the passive voice (present perfect passive).
- "No substitution required": Incorrect because the original "are assured" is passive and grammatically incorrect in this context.
- "have assured": Correct because it uses the active voice and agrees in plural number with "The authorities".

Thus, the grammatically correct sentence is: "The authorities have assured the people that they will look into the matter."