What are some primary contributors to background radiation?

cars, jets, and trains

televisions and computers

fossil fuels and oxygen

plants, animals, and cosmic rays

According to the big bang theory, after the "bang," the universe remained dark until about  300,000 yearsone billion yearsthree minutesthree billion years  later, when neutral atoms began to form.

Beth’s hygrometer is reading a temperature of 30 c and a relative humidity of 65%. the humidity in the air is?

What is the term for a water wave that is created by an underwater earthquake?