Which of the following is an example of physical change?
a. mixing baking soda and vinegar together, and this causes bubbles and
foam.
b. a glass cup falls from the counter and shatters on the ground.
c. lighting a piece of paper on fire and the paper burns up and leaves ashes.
d. baking a birthday cake for your mother.

Why is it important for scientists to review and repeat the work of other scientists? 1.a scientific theory must be tested three times before it is proven. 2.the scientific method only applies to repeated experiments. 3.an experiment may have had errors that the scientists didn't recognize. 4.the results of individual scientists may be influenced by bias. 5.an experiment must be performed twice before the data can be analyzed.