(C) Studi
Stemming chops off suffixes mechanically without checking meaning. For "Studies," the stemmer removes the suffix, producing "Studi" — not a real word, unlike lemmatization which gives "Study."
Stemming is a crude, rule-based process that strips affixes regardless of whether the result is a valid word. "Studi" is the classic example of stemming output for "Studies." This is also what distinguishes stemming from lemmatization — lemmatization would correctly return "Study." Examiners specifically test this distinction, so remember: stemming → "Studi" (may be meaningless); lemmatization → "Study" (meaningful root word).