Tara thought her backpack was too heavy. She decided to measure the mass of her backpack with her books and binder inside. Then she measured the mass of each individual thing that was inside her backpack. Finally, she found the mass of her empty backpack. She wrote all the masses in a table, shown below. Mass of Backpack & Items Inside Item Mass (in kilograms) math book 3 science book 2 binder 1 empty backpack 1 full backpack 7 Looking at the table, she noticed that adding up all the masses of the items in the backpack equaled the total mass of the full backpack. What did this demonstrate about mass? A. The mass of a full backpack does not depend on what is in it. B. The mass of a whole object is equal to the sum of the masses of its parts. C. The mass of a whole object is more than the sum of the masses of its parts. D. The mass of a whole object is less than the sum of the masses of its parts.