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

Ex Input:
Sentence: 'a blue and white train is coming down some tracks'. Replace the letter 'b' with 'u' in the sentence.

Ex Output:
a ulue and white train is coming down some tracks

Ex Input:
Sentence: 'an umbrella sitting on top of a hill next to a body of water'. Replace the letter 't' with 'b' in the sentence.

Ex Output:
an umbrella sibbing on bop of a hill nexb bo a body of waber

Ex Input:
Sentence: 'airplane flying in the sky on a dark night'. Replace the letter 'e' with 'w' in the sentence.

Ex Output:
airplanw flying in thw sky on a dark night