Which criteria and constraints do engineers need to consider when designing and constructing a physical reef model

the answer to your question is:

c. complementary base-pairing

50% lit on the left side

imagine a line passing through the center of earth that goes through both the north pole and the south pole. this imaginary line is called an axis. earth spins around its axis, just as a top spins around its spindle. this spinning movement is called earth's rotation. at the same time that the earth spins on its axis, it also orbits, or revolves around the sun. this movement is called revolution.