In this reported speech question on English grammar, a sentence is given in direct speech about starting a new assignment. Out of the four alternatives, select the option that best expresses the same idea in indirect speech: My colleague said, "I will start a new assignment tomorrow."

Introduction / Context:
Here the test focuses on reporting a future plan that was expressed in direct speech. In the original sentence, the colleague promises to start a new assignment "tomorrow". In reported speech, we must change both the future form with "will" and the time expression so that the sentence fits correctly into the past reporting situation. Such items are extremely common in competitive exams and measure whether you know the standard sequence of tenses in English grammar.

Given Data / Assumptions:

• The reporting verb "said" is in the past tense.
• The quoted clause contains "I will start a new assignment".
• The time word "tomorrow" refers to the day after the original day of speaking.
• The speaker is "my colleague", so "I" must become "he" in the reported sentence.
• The reported sentence should sound natural and preserve the idea of a future plan relative to the original time of speaking.

Concept / Approach:
When we report a future statement after a past reporting verb, "will" usually changes to "would". This keeps the meaning of future relative to the time of speaking but shows that we are reporting it later. Time words also need adjustment: "tomorrow" becomes "the next day" or "the following day". Pronouns are changed according to the subject of the reporting verb. We remove the comma and quotation marks, introduce the reported clause with "that", and keep the rest of the sentence structure and vocabulary unchanged so that the meaning stays the same.

Step-by-Step Solution:
First, remove the comma and quotation marks and join the clauses with "that". Second, change the pronoun "I" to "he" because the person speaking is the colleague. Third, backshift the future auxiliary "will" to "would" to match the past reporting verb "said". Fourth, replace the time word "tomorrow" with "the next day" to reflect the shift in time from when the sentence is being reported. Fifth, keep the rest of the words "start a new assignment" exactly as they are, preserving the intended meaning.

Verification / Alternative check:
The correct reported sentence "My colleague said that he would start a new assignment the next day" shows a future plan relative to the time of speaking in the past. The auxiliary "would" is the standard backshift of "will" in this context, and "the next day" accurately replaces "tomorrow". When read aloud, the sentence clearly means that at some earlier time your colleague said he intended to begin a new assignment on the following day. This confirms that the transformation follows accepted grammar rules.

Why Other Options Are Wrong:
Option A retains "tomorrow" and so does not properly change the time expression for reported speech. Options B and D keep "will", which does not show the expected backshift after "said" in the past. This creates a mismatch between the time of speaking and the time of reporting. Therefore they do not conform to the normal sequence of tenses. Only option C changes both "will" to "would" and "tomorrow" to "the next day" while also correcting the pronoun, so it is the only fully correct choice.

Common Pitfalls:
Candidates often remember to change "will" to "would" but forget to adjust time expressions like "tomorrow", "today", or "yesterday". Others may attempt to be too literal and keep the exact original words, ignoring the change in perspective that happens in reported speech. Some also forget to change the pronoun "I" to match the subject of the reporting verb. A good habit is to check every reported speech question for three things: pronoun change, correct tense backshift, and updated time or place words.

Final Answer:
The option that correctly converts the given direct sentence into reported speech is: My colleague said that he would start a new assignment the next day.