Generate a topic word for the given sentence. A topic word is usually the name of a person, place, animal, concept or object the sentence is focusing on.

Q: a rearguard is a part of a military force that protects the main force from attack from the rear.

A: rearguard
****
Q: defibrillation is the act of defibrillating the heart to treat the heart when it is not pushing blood because the heart muscle is not working in any pattern.

A: defibrillation
****
Q: crossed is a 2011 dystopian novel by ally condie.

A:
crossed
****