Question

ancient wall drawings in mammoth cave haven’t faded over time. the cave is safe from damaging environmental elements. because before if even though ← joining words combine the sentences into one sentence. use one of the joining words.

Explanation:

To combine the sentences, we need to show the causal relationship between the two statements. The first sentence (ancient wall drawings not fading) is a result of the second (cave being safe from damaging environmental elements), so "because" is the appropriate joining word. We structure the sentence to reflect this cause - effect relationship.

Answer:

Ancient wall drawings in Mammoth Cave haven't faded over time because the cave is safe from damaging environmental elements.