Final answer:
The word that begins with the same sound as 'knapsack' is 'backpack'.
Step-by-step explanation:
The word that begins with the same sound as 'knapsack' is 'backpack'. The 'b' sound at the beginning of 'backpack' is similar to the 'k' sound at the beginning of 'knapsack'. While 'keyboard' and 'notebook' also start with the letter 'b', they do not have the same initial sound as 'knapsack'.
Learn more about Finding words with similar initial sounds