Explanation:

- Sever: This means to cut off or divide by cutting. It's often used to describe the act of separating something into two parts.

- Option 1, Remove: To take something away or off from the position it occupies. This is more about extracting or deleting rather than dividing.

- Option 2, Trim: To make something neat or of the required size or form by cutting away irregular or unwanted parts. It's somewhat related but doesn't imply splitting apart.

- Option 3, Keep: To retain or hold on to something. It's not directly opposite to sever, but it implies not letting go or losing.

- Option 4, Unite: This means to come or bring together for a common purpose or action, making it the direct opposite of sever, which involves separation.

- Correct Answer: Unite