According to one management expert at CNBC, there’s one extremely revealing question that can seal the deal in a job interview. It’s simple: “What did you do to prepare for this interview?”

Suzy Welch, bestselling management author and CNBC contributor, says this question can become the deciding factor for employers. She loves it because it reveals a lot about candidates’ resourcefulness.

Suzy explained one example of how not to answer this question.

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“I had a candidate for executive assistant once who looked perfect on paper,” she said. “She had great experience, plus she aced my editing test. Our conversation was going merrily along, until I popped the question. Her surprised answer: ‘Um, I looked for your office on Google Maps.’ That was it. That was her prep.”

By contrast, another candidate had read all of Suzy’s books and columns, researched CNBC, and drove by the interview location the night before to check for parking.

Guess who Suzy ended up choosing?

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The better-prepared candidate, of course!

“I was like, ‘Wow, you started working on this job before you even got it,’” Suzy said. “I loved her resourcefulness and grit.”

If you’re a hiring manager, consider adding this question to your arsenal to get a better idea of what each candidate can bring to the table. And if you’re job-searching, this question provides an opportunity to shine, Suzy says.