Here are the answers to your questions:
Question 1: If someone says they are "feeling under the weather," that is an example of: An idiom
Question 2: “Just as a caterpillar transforms into a butterfly, we can grow and change through our experiences in life”, is an example of: An analogy
Question 3: When someone refers to a difficult situation as a "Herculean task," this is an example of: An allusion
Question 4: Which of the following sentences includes the 3 secret words we’ve encountered so far in Unit 6? It seems like the correct answer would depend on what the "3 secret words" are from your Unit 6 material. If I had that information, I could help identify the right sentence. Please provide those words, and I'd be happy to assist!