-  ‘in the eastern’ in place of ‘in eastern’

The error in the sentence is the use of the preposition "in" after the word "eastern part" in part (4) of the sentence. When we refer to a specific part of a country, we use the preposition "of" instead of "in". Hence, the correct sentence should be:

The new railway line will greatly improve transport and communication in the eastern part of the country.

Here, "the eastern part of the country" is a specific region, and the preposition "of" is used to show that it is a part of the country.

Let's understand the usage of prepositions "in" and "of" in detail:

• "In" is used to refer to a place that is enclosed or inside something. For example, "I am in the room."
• "Of" is used to indicate a relationship between two things, or to show possession or origin. For example, "The cover of the book" or "The people of the town".

In the given sentence, we are referring to a specific region, which is a part of the country. Hence, the correct preposition to use is "of".

Formula:

The correct preposition to use when referring to a specific part of a country is "of", not "in".

In conclusion, the correct answer is option (D), and the error in the sentence is in part (4), where the preposition "in" is used instead of "of".

If you think the solution is wrong then please provide your own solution below in the comments section .