The interview was a piece of cake. A hyperbole
B alliteration
C personification
D idiom
E simile
F metaphor
G onomatopoeia
H sensory imagery

D. Idiom

Explanation:

The phrase "piece of cake" is an idiom.

It's not a hyperbole because we're not exaggerating, it's not alliteration because the letters are not repeating, it's not personification because you are not giving a non living thing human characteristics.

It is not a simile because you're not using like or as, it's not a metaphor, it's not an onomatopoeia, or sensory imagery.

beneatha's hair symbolizes wealth  

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the answer to the question is a