Which of the Following Accurately Characterizes the State of Most

question 52

Multiple Choice

Which of the following accurately characterizes the state of most of the hydrogen in the Universe from the time of Big Bang nucleosynthesis to the present day?

• A) neutral, then ionized, then neutral
• B) neutral, then ionized
• C) ionized, then neutral, then ionized
• D) ionized, then neutral

---

Definitions:

Clock Proteins

Molecular components that constitute the biological clock, regulating circadian rhythms in organisms by oscillating in a 24-hour cycle.

Biological Clocks

Mechanisms by which activities of organisms are adapted to regularly recurring changes in the environment. See circadian rhythm.

Feedback Loops

Systems within biological and ecological processes that regulate themselves through cycles of feedback information.

Sign Stimulus

A specific trigger from the environment that elicits an innate behavior in an animal.