In this task, you need to replace a letter in the sentence with another given letter.

Sentence: 'a couple of brown bears walking across a lush green field'. Replace the letter 'w' with 'o' in the sentence.
a couple of broon bears oalking across a lush green field

Sentence: 'a horse in a country field with woods in the background'. Replace the letter 'a' with 'i' in the sentence.
i horse in i country field with woods in the bickground

Sentence: 'there is a truck full of people in front of a building'. Replace the letter 'i' with 'y' in the sentence.

there ys a truck full of people yn front of a buyldyng