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

Example Input: Sentence: 'a crowd watches as giraffes graze the tree tops at the zoo'. Replace the letter 't' with 'q' in the sentence.
Example Output: a crowd waqches as giraffes graze qhe qree qops aq qhe zoo

Example Input: Sentence: 'a study features the color green and old-fashioned furniture'. Replace the letter 'e' with 'd' in the sentence.
Example Output: a study fdaturds thd color grddn and old-fashiondd furniturd

Example Input: Sentence: 'a white fence stands near train tracks as two trains are in the distance'. Replace the letter 'a' with 'd' in the sentence.
Example Output:
d white fence stdnds nedr trdin trdcks ds two trdins dre in the distdnce