Please help!! Multiple choice question.

The image shows embryos of three vertebrate classes

Describe at least 2 abiotic and two biotic factors found in the desert biome how do these abiotic factors interact with the biotic factors

The circles, or orbits, for electrons are called energy levels. each level can hold only a certain number of electrons. add electrons to each level until you can't add any more. how many electrons can each level hold?