Final answer:
The incorrect part of the sentence is the adjective 'bonito', which should be 'bonita' to agree with the noun 'muchacha'.
Step-by-step explanation:
The part of the sentence that is not correct is bonito. In Spanish, adjectives must agree in gender and number with the noun they modify. Since muchacha is a feminine noun, the correct form of the adjective bonito should be bonita. Therefore, option D is the incorrect part of the sentence.
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