It is the same element that it was before with no measurable change in mass which kind of Decay has occurred and how do you know After a radioactive atom decays

altitude, density, pressure

air gets less dense the higher the altitude and also the air pressure is less as altitude rises.

the role of the microscope world in creating new materials .

the answer is b because, investigating whether another species of moth also drinks tears might be interesting, but it would not directly explain why this species of moth does.

to explain why this species of moth drinks tears, the scientist could ask: "what nutrients that moths need are in elephant tears? "

the scientist could experiment with moth repellent or oter ways to keep the moths away, but that would not answer his original question.