TASK DEFINITION: In this task, you need to replace a letter in the sentence with another given letter.
PROBLEM: Sentence: 'a table full of various types of cellphones, pdas and pagers'. Replace the letter 's' with 'f' in the sentence.

SOLUTION: a table full of variouf typef of cellphonef, pdaf and pagerf

PROBLEM: Sentence: 'the bus is trying to navigate though the london traffic'. Replace the letter 'a' with 'l' in the sentence.

SOLUTION: the bus is trying to nlviglte though the london trlffic

PROBLEM: Sentence: 'a baby lying in the lap of a large white teddy bear'. Replace the letter 'a' with 'r' in the sentence.

SOLUTION:
r brby lying in the lrp of r lrrge white teddy berr