within the trachea, the __ contains mucous glands that secrete mucus onto the epithelial surface through secretory ducts

answer; /// the correct )

currents is the correct answer.

but there is no

i guess you forgot putting it.

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.