Answer:
d) 10
Explanation:
Caesar cipher is code that uses the shift of the letters of alphabet. Key size simply denotes the number of the letters shifted.
For example, let's take the letter A. If key size iz 3, A becomes D (third letter down the alphabet). If the key size is 6, A becomes G (sixth letter down the alphabet).
So to answer this question, we need to decode this code. That means we do reverse process; we go up the alphabet, and shift every letter in the code for the key size.
If the key size is 3, we shift every letter of the code by 3 up the alphabet. So, Z becomes W, E becomes B etc. We end up with: WBALMMVYANLAYLZBSA which obviously doesn't make any sense.
If the key size is 5, similarly, we end up with: UZYJKKTWYLJYWJXZQY.
If the key size is 7, we end up with: SXWHIIRUWJHWUHVXOW.
And finally if the key size is 10, we end up with: PUTEFFORTGETRESULT (PUT EFFORT GET RESULT), which is the only option that makes sense.
