Few musicians have an attitude of humor about themselves, although a touch of this joke humor self hoax can boost sales.

The others are out of scope.

Hope now is clear to you.
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The hint here is the phrase "laugh at themselves" which means to not take oneself too seriously and be able to find humour at your actions.
Out of the options given:- embarrassment, self-doubt and cynicism do not fit the mood of the sentence which is positive.
Congeniality can be a close match which means to be affable or friendly. But here the point is that rock stars should be able to find mirth in their action and not about being friendly. Hence , self-deprecation fits the bill.

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.
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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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