The correct answer is D. The Spartans worked to stop a second Persian invasión of Greece.
Step-by-step explanation
The battle of the Thermopylae was a battle of the Second Greco-Persian Wars, this battle took place in the narrow passage of Thermopylae in the middle of 480 A.C. and lasted seven days. It started when the Persian led by Xerxes I, wanted to dominate the Greece territory through invasion. As a reaction, several Greek Polis were allied, including Sparta and Athens. Those greek people fought against the Persians to stop the second invasion of the Persian Empire. So, the correct answer is D. The Spartans worked to stop a second Persian invasion of Greece.