(plz anwser all questions 15 points)

question 1: check all the statements that are correct. conservation of mass means:

a: we can start a reaction with different types of elements than we have at the end of the reaction.

b: matter cannot be created

c: matter can be destroyed in a chemical reaction

d: we must start and end with the same amounts of matter

question 2: select all of the signs of a chemical reaction

a: a gas is released

b: a solid is formed

c: a temperature change happens

d: the change can be easily undone

e: the state of matter changes

f: a color change happens