Background extinction refers to the normal extinction rate. These are species that go extinct simply because not all life can be sustained on Earth and some species simply cannot survive. Mass extinction is a widespread event that wipes out the majority (over 50%) of living plants and animals.
Some unicellular organisms are similar to animals because they have the ability to move.
Third option
A short period of time, after the onset of puberty. The first mature eggs starts to be released from the ovaries during menstruation. Menstruation may first occur during the start of puberty in women, it may start as early as 8 years old and can start late as 16 years old. Menstruation is the process wherein not fertilized eggs are being broken down and released from the body.
