Audible beats are formed bu the interference of two waves
a. of slightly different frequencies
b. of greatly different frequencies
c. with equal frequencies, but traveling in opposite directions
d. from the same vibrating source.

Which statements identify what astronomers currently know and think will happen with our universe? check all that apply. the big bang produced dark energy, which accounts for some of the energy needed to expand the universe. the vastness of space may contain a type of matter known as "dark matter." the universe is currently shrinking at a rapid rate. the universe is currently expanding at an accelerating rate. the big bang theory explains all the energy and matter discovered by scientists.