Final answer:
Esther's unique act of resistance in the book 'Resistance' was d) saving Chaya's life. This is distinct from the collective resistance efforts such as uprisings and joining the resistance movements of the time.
Step-by-step explanation:
In the book Resistance, the one thing Esther came up with that she had done that no other had done is (d) Saving Chaya's life.
While escaping from the Lodz Ghetto, joining the ZOB, and surviving the Warsaw Ghetto Uprising were acts of resistance and survival that many were involved in, the specific act of saving Chaya's life was unique to Esther.
During this period, examples of resistance in various forms took place throughout the Holocaust; these included uprisings, espionage, saving children, and other individual acts of heroism and defiance against Nazi power.