If not as an element, atoms show up as and One of the most important compounds is water,

2. It is a major part of the (as )

3. Most of the is water (as )

4. It is required for chemical and energy production (called a reaction)

Which best describes the present-day universe? opaque, expanding very slowly, stars produce heavy elements transparent, expanding at an accelerated rate, stars produce heavy elements opaque, expanding at an accelerated rate, stars produce only hydrogen and helium transparent, expanding very slowly, stars produce only hydrogen and helium