An Average of the masses of all the isotopes that occur in nature for an element is the?

This active feature of earth's crust in building mountain ranges as well as islands. this feature is a a) cavern. b) earthquake. c) mountain. d) volcano.

All cells are made of four types of acids, lipids, proteins, and carbohydrates.

Which statement correctly identifies the scientific question and describes why the question is scientific? question 1 refers to the supernatural.question 2 reflects a moral or social value.question 3 refers to something that can be measured.question 4 reflects a question that can’t be observed.