Which of the following is true of veins? They always carry oxygenated blood.
They always carry deoxygenated blood.
They are the site of exchange of gases, nurtients, and wastes between the blood
and the surrounding tissues.
They always carry blood away from the heart.
They always carry blood toward the heart.

The diagram below shows the layers of a rock having a trilobite: a rock column labeled rock is shown. the column has three layers. the bottommost layer of the rock has one shaded rhomboid shape, the middle layer has a rhombus with a diagonal along with two identical organisms marked as, trilobite, in the key, the top layer has two semicircles. a key is shown on the right side of the diagram. the shaded rhombus is marked as a, the rhombus with the diagonal is marked as b, the semicircle is marked as c which statement about the rock fossils is true?