Teacher: In this task, you will be presented with a context passage, a question about that paragraph, and a possible answer to that question. The task is to check the validity of the answer. Answer with "Yes" or "No".
Teacher: Now, understand the problem? If you are still confused, see the following example:
Timothy likes to play sports. He spends his time after school playing basketball and baseball. Sometimes Timothy pretends he is a famous baseball pitcher for his favorite team with his friends. He plays with his friends Mandy and Andrew. Timothy also plays pretend when he is alone. He has an imaginary friend named Sean. Sean is an elephant who watches television with Timothy. Mandy likes playing baseball but she also likes to paint. Mandy's favorite class at school is art. She likes making pictures of flowers. Her teacher says she is a good artist. She painted a picture of a tree for her teacher. There were red and yellow leaves on it. It had apples on it. When Andrew goes home after baseball, he likes to eat a snack. He eats carrots and bananas. If he is a good boy his mom, Mrs. Smith, sometimes gives him milk and cookies. Afterwards, Andrew finishes his homework. <sep>Who does Timothy play with?<sep>Basketball and baseball
Solution: No
Reason: Based on the passage Timothy plays with his friends Mandy and Andrew. So, the given answer is incorrect and the output should be "No".

Now, solve this instance: Before crossing to Asia, Alexander wanted to safeguard his northern borders. In the spring of 335 BC, he advanced to suppress several revolts. Starting from Amphipolis, he traveled east into the country of the "Independent Thracians"; and at Mount Haemus, the Macedonian army attacked and defeated the Thracian forces manning the heights. The Macedonians marched into the country of the Triballi, and defeated their army near the Lyginus river (a tributary of the Danube). Alexander then marched for three days to the Danube, encountering the Getae tribe on the opposite shore. Crossing the river at night, he surprised them and forced their army to retreat after the first cavalry skirmish. News then reached Alexander that Cleitus, King of Illyria, and King Glaukias of the Taulanti were in open revolt against his authority. Marching west into Illyria, Alexander defeated each in turn, forcing the two rulers to flee with their troops. With these victories, he secured his northern frontier. While Alexander campaigned north, the Thebans and Athenians rebelled once again. Alexander immediately headed south. While the other cities again hesitated, Thebes decided to fight. The Theban resistance was ineffective, and Alexander razed the city and divided its territory between the other Boeotian cities. The end of Thebes cowed Athens, leaving all of Greece temporarily at peace. Alexander then set out on his Asian campaign, leaving Antipater as regent. <sep>What two groups did Alexander defeat in order to secure the northern frontier?<sep>The Illyrians and the Taulanti
Student:
Yes