Concept:Change each vowel to the second letter after it and each consonant to the previous letter, then count the new clusters that have no vowel.
Explanation:Original clusters:
CAB, BIT, YET, AFT.
Apply the given transformation to each letter:
CAB→BCA because
C→B,
A→C,
B→A.
BIT→AKS because
B→A,
I→K,
T→S.
YET→XGS because
Y→X,
E→G,
T→S.
AFT→CES because
A→C,
F→E,
T→S.
Now check vowels in the new clusters:
BCA has
A, so it contains a vowel.
AKS has
A, so it contains a vowel.
XGS has no
A, E, I, O, U, so it has no vowel.
CES has
E, so it contains a vowel.
Therefore, exactly one cluster has no vowel.
Answer:One cluster. Correct option: D.