I believe it is 4)Shearing teeth (Carnassial teeth)
Amniotic egg are for reptiles
Fur are for marsupials, and dogs
Retractable claws are are cats
Shearing teeth are for carnivores
It is important because you need vitamins and minerals from them e.g. Scurvy no vitamin c
'Red shift' is a key concept for astronomers. The term can be understood literally - the wavelength of the light is stretched, so the light is seen as 'shifted' towards the red part of the spectrum.
Hope this helps.
