Gamma radiation can be significantly reduced by… A sheet of paper

Air

A 3 mm thickness of aluminium

Several cm of lead

May someone explain how to do this question?

30 points - when can a theory be modified if a new type of technology allows for new observations that raise new questions? a. immediately, while the questions about the theory are being asked b. after new hypotheses related to the theory are tested in experiments c. only after the new observations disprove all parts of the theory d. while scientists begin to think about how the theory could improve

In an experiment, how can i change human errors? be specific.