The spleen and the thymus work together to fight infection. These organs together make up which next level of organization?

The table shows dates and appearance of index fossils. which rock layers can be dated most precisely? a) a layer containing both a fossil 4 and a fossil 3 b) a layer containing both a fossil 2 and a fossil 3 c) a layer containing both a fossil 1 and a fossil 4 d) a layer containing both a fossil 1 and a fossil 2

The kind of fertilization found in the majority of aquatic animals is (internal or external) fertilization.

Which layer will become saturated first when rain falls?