What makes dark energy "dark"?

Aits unknown nature
Bits completely black color
Cits existence beyond the visible spectrum
Dits inevitable creation of a totally destructive Big Crunch

Nucleosynthesis began when _____ and ended when _____.

Athe Big Bang occurred; the Big Crunch occurred
Bnuclear reactions could first occur; matter had condensed into galaxies and stars
Cthe cosmic microwave background radiation formed; dark energy replaced it as the dominant energy form
Dthe universe had cooled enough for atoms to combine; protons and neutrons were too far apart to form nuclei