The example that uses proper, according to MLA standards, in-text citation is the following:
D. Nutritionist Soon-yu Kim describes whole foods as the "cornerstone of a healthy diet" (23)
MLA format follows the author-page method of in-text citation; it requires the author's last name and the page number. If the name appears on the sentence itself, then only the page number should be in parentheses at the end of the sentence (this is the reason why A, which provides redundant information as the last name was already present on the sentence, and C, which places the page number close to the author's name, are incorrect).
