Read this excerpt from A Black Hole is NOT a Hole. As you take off, remember: predicting the exact details of your journey is tricky. After all, no one has ever visited a black hole, and we can’t send a probe in to take a peek and send the information back to us. Not even sneak previews can escape from a black hole.

What is the author doing by using the phrase "Not even sneak previews can escape from a black hole"?

A defining space travel
B describing the history of astronomy
C defining a black hole
D describing the purpose of a probe