Shields are:_______.a. composed of rocks that were metamorphosed during recent (less than a million years ago) mountain-building events. b. composed of some of the oldest rock on the Earth. c. rarely exposed at the Earth's surface and contain blueschist. d. composed of extensive areas of sedimentary layers laid down on lava flows.
Explanation: shields are layers of old rocks that metamorphosed as a result of mountain-building events. Shields also have sedimentary layers that usually rest on the lava of the rock.
