The diagram shows the fossils found in different layers of a rock.

A diagram labeled Fossil Layers is shown. The topmost layer is labeled A and shows the skeleton of a fish, the second layer from the top is labeled B and shows a shell, the third layer from the top is labeled C and shows a fern leaf, and the lowermost layer shows an oak leaf

In which layer is the oldest fossil found?

Group of answer choices

Layer A

Layer B

Layer C

Layer D

The health, management and conservation of biodiversity, is a challenge facing ecosystems worldwide. the major factors that affect the health and function of the great barrier reef are climate change and pollution. which question investigates the effects of a biotic factor on the reef ecosystem?

Which is an advantage of having memory cells when a pathogen is encountered for a second time. a) the memory cells are what proliferate into clones of cells in response to the binding of an antigen. b) memory cells are vital to the primary immune response in that they immediately recognize pathogens even at the first encounter. c) memory cells are essentially effector cells that are short lived and attack antigens even without having a receptor specific to that antigen. d) it ensures that more lymphocytes with a receptor specific to a particular antigen will be present than in a host that had never encountered that pathogen.

Match the description of each organism to the appropriate category