Read the following excerpt from Mrs. Drainger's Veil by Howard Mumford Jones:

Emily, of course, had changed. She met me at the door as she met you. She was a shell burned out by one fierce moment of fire.

Metaphor.

Euphemism.

Alliteration.

Flashback.

The correct answer is A. metaphor. A metaphor is a rhetorical figure of speech in which two things are compared without using words such as like or as. So here, Emily is being compared to 'a shell burned out by one fierce moment of fire' - she's not an actual shell, but rather compared to one through the use of a metaphor.