This question consists of a sentence which is divided into four parts numbered (1) to (4). Only one part of the sentence is not acceptable in standard writing English. Identify that part which contains an error.

Correct option is A

The phrase "They are living in Delhi" is incorrect in the context because the present continuous tense "are living" is not appropriate for an action that has been continuing for a long duration like two decades. The correct tense should be present perfect continuous tense, as it indicates an action that started in the past and continues in the present.
Corrected sentence: "They have been living in Delhi for two decades now and yet find it difficult to locate places in it."
Grammatical rule used:
The present perfect continuous tense is used to describe actions that began in the past and are still ongoing. Hindi Explanation: जब कोई कार्य अतीत में शुरू हुआ हो और अब भी चल रहा हो, तब Present Perfect Continuous Tense का प्रयोग किया जाता है।
Example:
Incorrect: He is working in this company for five years. Correct: He has been working in this company for five years.