Directions: Read the following sentences carefully and select the one that is grammatically correct and free of any error. If all the given sentences contain errors, select "All are incorrect".

Which of the given sentences is error-free?

The correct answer is: The inauguration of the regional research facility marks a significant milestone in national scientific progress.

Explanation:

Let us analyze each sentence to determine its correctness:

1. "The new solar power plant will enables local enterprises to reduce their energy costs."
Incorrect: The modal auxiliary verb "will" must be followed by the base form of the main verb ("enable"). Using "enables" is grammatically incorrect. The correct phrase is "will enable".

2. "Environmental groups has called upon the council to clean the lake and enforce strict pollution regulations."
Incorrect: There is a subject-verb agreement error. The subject "Environmental groups" is plural, so it requires the plural auxiliary verb "have" rather than the singular verb "has". The correct phrase is "Environmental groups have called".

3. "Heavy rainfall disrupted transport logistics, forcing suppliers to delaying scheduled shipments."
Incorrect: The infinitive form of the verb should be used after "to". Using the gerund form "delaying" is incorrect here. The correct phrase is "to delay scheduled shipments".

4. "The inauguration of the regional research facility marks a significant milestone in national scientific progress."
Correct: This sentence is grammatically correct and completely free of errors. The singular subject "The inauguration" agrees properly with the singular verb "marks".

Therefore, this option is the error-free sentence.