The idiom 'icing on the cake' means— (49th Special BCS)
কa slice of the cake
খan attractive but unnecessary addition✓
গan attractive service
ঘan attractive and essential enhancement
ব্যাখ্যা
Idiomatic expressions reflect how language users think metaphorically about common experiences.
Idiom: "Icing on the cake" (also "Frosting on the cake")
Meaning:
Something extra that makes a good situation even better, but is not absolutely necessary. It is a desirable addition on top of something already satisfying — much like icing/frosting on a cake: the cake is good without it, but icing makes it even nicer.
Usage examples:
— "Getting a bonus was great, but the office party was the icing on the cake."
— "She won the competition, and the scholarship was just the icing on the cake."
Nuance:
The key element is that the icing is EXTRA — pleasant but not essential. The cake (the main benefit) exists independently.
Distinguishing from similar expressions:
— "Cherry on top" = similar meaning; the best part of something already good
— "Cream of the crop" = the best among many
Why option (D) is wrong:
✗ "essential enhancement" — the icing is specifically NOT essential; thats the point of the metaphor
Source: Oxford Dictionary of Idioms; Cambridge Idioms Dictionary.