Sarah and Maria made a telephone using two cans and a string. They pulled the string tight and Maria went out into the hallway. When Maria spoke into her can, Sarah could hear her because the sound waves
Atravelled through a vacuum.
Eliminate
Btravelled from the cold hallway to the much warmer classroom.
Ctravelled from the vibrating can through the string to the other can.
Dtravelled through the air from Maria to Sarah even though they were in different places.
I think it's either C or D because things make to many noise that can change one of the girls' that can make vibration, so I think the best answer is C. Hope this helps :) If any confusion, please feel free to contact me anytime :)
