It seems we must all sleep in ________ to maintain normal levels of skills.

• A. order
• B. lines
• C. groups
• D. sequences

Answer: (A)

This item tests a phrase that expresses purpose. The natural way to say why we do something is to use “in order to,” which introduces a purpose clause.

So the blank should be filled with order to form the familiar expression “in order to,” giving: It seems we must all sleep in order to maintain normal levels of skills. This sounds natural and clear, meaning sleep is necessary for maintaining skills.

The other options don’t fit because they don’t form a natural collocation with “sleep in” or convey purpose here; they’d sound odd or create an illogical image.