Final answer:
Prepositions can appear without complements in expressions or intransitive verbs. 'On' in 'He is on his way' and 'out' in 'He sneaked out' are examples where the preposition has no clear object.
Step-by-step explanation:
Prepositions can appear without complements in certain situations, such as when they are part of an idiomatic expression or when they follow an intransitive verb that does not require a direct object. For example, in idiomatic expressions like 'He is on his way,' the preposition 'on' has no complement. With intransitive verbs, the preposition may be part of a phrase that provides adverbial information but is not strictly a complement to the verb. In the case of 'He sneaked out,' the word 'out' acts as an adverbial component of the prepositional phrase, providing context but not serving as a direct complement.
In instances where a prepositional phrase serves as a subject complement, the preposition 'like' often precedes a noun phrase, as in the sentence 'She appeared like an expert.' Here, the prepositional phrase 'like an expert' functions as a subject complement describing the subject 'She.' Additionally, in some cases, prepositions may end a sentence where the object is understood or implicit, particularly in conversational English, such as in 'What are you talking about?'