Question

native americans have known about mammoth cave for 5,000 years. european settlers claimed to discover mammoth cave in 1790. until if even though because ← joining words ① combine the sentences into one sentence. use one of the joining words.

Explanation:

We need to combine the two sentences using a joining word that shows a contrast. "Even though" is suitable as the first sentence says Native Americans knew about the cave for 5,000 years, and the second says European settlers claimed to discover it in 1790, which is a contrasting situation. So we structure the sentence with "even though" to connect them.

Answer:

Even though Native Americans have known about Mammoth Cave for 5,000 years, European settlers claimed to discover Mammoth Cave in 1790.