Why A
isnt a similar to D also ?

No

Self-deprecation is a critic you do on yourself.

D instead is when you cat or do something which creates you a not comfortable situation towards the other people.

Comparatively few rock musicians are willing to laugh at themselves, although a hint of_____can boost sales of video clips very nicely.

The sentence states that comparatively few rock musicians are willing to laugh at themselves. Which means most rock musicians are "not willing to laugh at themselves". It then contrasts this attitude with yet another disposition which involves a "hint of __________" that can boost sales of video clips very nicely. So the word/phrase for the second blank should be "willingness to laugh at oneself".

congeniality is being warm, friendly and affable.

cynicism is a negative word and is too extreme, the willingness to laugh at oneself is nowhere mentioned to be the result of a negative attitude.

embarrassment is again not the same as being willing to laugh at oneself.

willingness to laugh at oneself is not the result of self-doubt, but an attitude resulting from a willingness to be critical of oneself.

self-deprecation is what happens when you willing laugh at your flaws, mistakes or other imperfections. And this is a conscious act. Hence the correct choice.

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