Detailed Instructions: You are given a paragraph, a question and some answer options (associated with "A", "B", "C", "D", etc.) You need to list all the correct answer options with their associated letters (e.g. "A" can be a valid answer). Note that sometimes, more than one option can answer the question correctly and completely. In those cases, please generate all such options separated by a comma (e.g. "A, B" is a valid answer). Do not generate anything else apart from one or more of the following characters: 'A', 'B, 'C', 'D', etc.
Problem:Paragraph- Sent 1: The idea that Earth is a magnet is far from new.
Sent 2: It was first proposed in 1600 by a British physician named William Gilbert.
Sent 3: Knowing it acts like a magnet is one thing.
Sent 4: Knowing why it acts like a magnet is more difficult.
Sent 5: In fact, finding out why is a fairly recent discovery.
Sent 6: To find out why required new technology.
Sent 7: It was the seismograph that made it possible to learn why the Earth acted like a magnet.
Sent 8: Seismograph are used to study earthquakes.
Sent 9: By studying earthquake waves they were able to learn about Earths interior.
Sent 10: They discovered that Earth has an inner and outer core.
Sent 11: The outer core consists of liquid metals, mainly iron and nickel.
Sent 12: Scientists think that Earths magnetic field is generated here.
Sent 13: It is caused by the motion of this liquid metal.
Sent 14: The liquid metal moves as Earth spins on its axis. 
Question: What technology made it possible to test the Earth's magnetic properties? How were scientist able to use this machine to study this phenomenon? (A) Earth has an inner and outer core. The outer core consists of liquid metals, mainly iron and nickel. Scientists think that Earths magnetic field is generated here (B) Tomograph, analized infrared images (C) Seismograph, studied earthquake waves (D) Seismograph, Seismograph are used to study earthquakes.
Sent 9: By studying earthquake waves they were able to learn about Earths interior (E) It was the seismograph that made it possible to learn why the Earth acted like a magnet. Seismograph are used to study earthquakes. By studying earthquake waves they were able to learn about Earths interior.
Solution:
C, D, E.