One way to understand the role of sleep is to look at ________ happens if we don't get it.

One way to understand the role of sleep is to look at ________ happens if we don't get it.

• A. that
• B. how
• C. what
• D. when

Answer: (C)

The key idea here is using what to introduce a content clause after a phrase like look at. In this sentence, what stands for “the things that,” so the pair look at what happens describes examining the consequences or events that occur if we don’t get sleep. That makes the sentence natural and complete: you’re directing the listener to consider the specific outcomes. Why the other options don’t fit: that wouldn’t give a natural follow-up to look at in this context, and how or when would produce awkward or ungrammatical phrases (look at how happens / look at when happens). The structure with what is the smooth, idiomatic choice for referring to the events involved.

The key idea here is using what to introduce a content clause after a phrase like look at. In this sentence, what stands for “the things that,” so the pair look at what happens describes examining the consequences or events that occur if we don’t get sleep. That makes the sentence natural and complete: you’re directing the listener to consider the specific outcomes.

Why the other options don’t fit: that wouldn’t give a natural follow-up to look at in this context, and how or when would produce awkward or ungrammatical phrases (look at how happens / look at when happens). The structure with what is the smooth, idiomatic choice for referring to the events involved.