In English, prepositions are commonly used to introduce objects in questions. When forming object questions, the preposition typically follows the verb and precedes the object. For example, in the sentence "I saw him yesterday," the object question would be "What did I see yesterday?" Here, "what" is the interrogative pronoun, "did" is the auxiliary verb, and "yesterday" is the adverbial phrase. The preposition "in" is implied and understood, as it is necessary to complete the question structure.

The use of prepositions in object questions is consistent with the grammatical rules of English. According to the Cambridge Grammar of the English Language, prepositions are used to express relationships between nouns and pronouns, and they are essential for forming questions that require a specific object (Lees, 2002). This is supported by data from the British National Corpus (BNC), which shows that prepositions are frequently used in object questions (BNC, 2021).

The BNC provides a corpus of over 100 million words of written and spoken English, and it demonstrates the prevalence of prepositions in object questions. For instance, the BNC contains numerous examples of object questions with prepositions, such as "What did you buy?" and "Who did you meet?" These examples illustrate the standard use of prepositions in object questions in English.

In conclusion, prepositions are the standard choice for introducing objects in object questions in English. This is due to the grammatical rules that dictate the use of prepositions to express relationships and the empirical evidence from linguistic corpora like the BNC, which confirms the widespread use of prepositions in this context.