Answer:
1). During class.
2). Across the room.
3). Above the lake.
Explanation:
Prepositional phrases are described as the phrases that consist of a preposition, its object(which could be a noun, gerund, pronoun, or clause), and any modifiers to modify the object.
In the given sentences, the prepositional phrases are 'during the class', 'across the room', 'above the lake' as they justify the above definition and act as a function either as adjectives or adverbs to qualify a noun, pronoun, or a verb.
In order to make the structure more complex, the sentences could be written as:
1). You should consider taking notes during class before it gets too late.
2). Crystal could hear her sister snoring across the room despite the blaring sound of music playing in her room.
3). The flying saucer appeared above the lake before it disappeared into the mysterious space forever.
