Answer: A
Explanation: Stainless steel
They study rocks from both the moon and the earth
Not the plants but the soul could be made into mud in both past and present. In past, most houses(not in the US) but in many countries were made up of soil. But know in present, soil or even mud is used to put it in the concrete to make the building strong in many countries like India. Good luck:)
Help them conduct research on them for their study