Step 1: Understanding the Concept.
A quick way to find the object of a sentence is to first find the verb, then ask "what" right after it. Step 2: Key Formula or Approach.
Find the verb in the sentence, then ask "the subject verbs what?" The word that answers this question is the object. Step 3: Detailed Explanation.
The verb here is "sells." Ask, "the shopkeeper sells what?" The answer is "lemons." So "lemons" answers the "what" question and is the object of the verb "sells."
"Shopkeeper" answers "who sells," so that word is the subject, not the object. There is only one verb in the sentence, "sells," so "lemons" cannot be the verb. The predicate is everything said about the subject, "sells lemons" as a whole, not just the single word "lemons." Step 4: Final Answer.
Since "lemons" answers "sells what," it is the object of the sentence, matching option (A).