Which of the following statements is true? Observations are often used to form questions about the world.
The dependent variable is changed by the experimenter.
The best hypotheses are written as answers to a question.
A hypothesis is created at the end of an experiment.

Which statements best describe the work of marie and pierre curie? check all that apply. they discovered radioactivity. they came up with the term “radioactivity.” they conducted experiments with uranium-containing minerals and pure uranium. they conducted experiments with uranium-containing minerals and photographic plates. they discovered two new radioactive elements.