What is formed when two or more different kinds of atoms or elements join together chemically

Why is alternating current more effective at long–distance travel than direct current? a. the power lines are made out of conductors. b. transformers increase or decrease voltage as needed. c. the ac generator is more efficient. d. ac has lower voltage than dc.

What is an aquifer for science class

Could we see a galaxy that is 20 billion light-years away?