Select the most appropriate option that can substitute the highlighted word segment in the given sentence.
Neha is writing a letter when I called her.

Correct option is D

The correct substitution is (d) was writing.
Explanation: The sentence has two actions – "was writing" and "I called". Both occurred in the past, so past continuous should be used for the ongoing action and simple past for the interrupting one.
Correct Structure:
Past Continuous (ongoing) + when + Simple Past (interruption)
Example: She was reading a book when I knocked.

Information Booster:
Use past continuous tense for an action in progress when another action interrupts it in past simple.