Take another look at the sentence:

The computer began to wail like an ambulance, startling poor Robert, who only wanted to retrieve his paper, unfortunately, a virus had immobilized the hard drive.

Who only wanted to retrieve his paper is a relative clause. Although it has a subject, who, and a verb, wanted, it does not express a complete thought. You must attach relative clauses to main clauses if you want to avoid writing fragments. In the sentence above, the relative clause is attached to the main clause that opens the item, The computer began ....

When a subordinate clause follows a main clause, you usually do not use a comma between the two. Who clauses, however, are a special case. Because Robert is specific, you need to use a comma between Robert and who. See Comma Tip 5 for more information.

Go back to the sentence to try again.

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