The question asks us to identify the one sentence that is different from the other three among the given four sentences. To do this, we need to analyze each sentence's meaning, structure, and the type of information it conveys.

Sentence Analysis and Comparison

Let's examine each sentence carefully:

• A. Deforestation causes soil erosion.

  This sentence states a general scientific or environmental fact. It describes a cause-and-effect relationship between a broad process (deforestation) and its environmental consequence (soil erosion). While human activity often leads to deforestation, the sentence itself focuses on the process and its general impact, not a specific, discrete action performed by an individual.

• B. The magician performed a trick.

  This sentence describes a specific action performed by a particular individual (the magician). It refers to a discrete event where a human agent carried out an action at a particular time.

• C. The patient was looked after by the nurse.

  This sentence describes a specific action performed by a particular individual (the nurse) on another individual (the patient). It details a discrete event involving specific human actors. This sentence is also notable for being in the passive voice, where the subject (the patient) receives the action.

• D. Karan gave me a book.

  This sentence describes a specific action performed by a particular individual (Karan) for another individual (me). It refers to a discrete event involving specific human agents at a particular time.

Sentence Distinctions

Upon comparing these sentences, we can observe a key difference:

• Sentences B, C, and D all describe specific, discrete actions or events involving identifiable individual human beings (magician, nurse, patient, Karan) as direct agents or recipients of the action. They narrate particular happenings or occurrences.
• Sentence A, "Deforestation causes soil erosion," on the other hand, expresses a general, factual statement about a widespread process and its environmental outcome. It does not describe a single, specific event performed by a named individual at a particular time. Instead, it presents a universal truth or a general causal link, making it different from the specific event descriptions.

Therefore, based on the nature of the statement – whether it describes a specific, discrete human-centric action/event versus a general fact/process – sentence A stands out as the different one.

The sentence that is different from the others is A. Deforestation causes soil erosion.