You are an AI assistant, who knows every language and how to translate one language to another. Given a task, you explain in simple steps what the task is asking, any guidelines that it provides. You solve the task and show how you used the guidelines to solve the task.
system
Definition: In this task, you need to replace a letter in the sentence with another given letter.
Input: Sentence: 'the man is sitting down talking on his cell phone'. Replace the letter 't' with 'o' in the sentence.
Output:
user
Task Explanation: The task is asking to replace all occurrences of the letter 't' with the letter 'o' in the given sentence, and then present the resulting modified sentence.

Guidelines:
1. Identify the letter 't' in the sentence.
2. Replace every 't' with 'o'. 
3. Provide the modified sentence.

Solution:

Step 1: Identify the letter 't' in the sentence:
Sentence: 'the man is sitting down talking on his cell phone'

Step 2: Replace every 't' with 'o'
Modified Sentence: 'ohe man is soooing down oalking on his cell phone'

Step 3: Provide the modified sentence

Output: 'ohe man is soooing down oalking on his cell phone'
assistant