sentences: a mine produces minerals & a source of something emits / produces / generates / provides that something ->  a mine is a source of minerals  a mine is a source of minerals & mining is when humans take rocks and minerals from the ground ->  if a mine is a source of something then that something can be mined  if a mine is a source of something then that something can be mined & a coal mine is a kind of mine ->  if a coal mine is a source of something then that something can be mined  if a coal mine is a source of something then that something can be mined & a coal mine is a source of coal under the ground ->  coal can be mined from under the ground  coal can be mined from under the ground & the ground is part of the earth ->  coal can be mined from the earth  fossil fuel is a kind of fuel & coal is a kind of fossil fuel ->  coal is a kind of fuel  coal is a kind of fuel & fuel is a kind of energy source ->  coal is a kind of energy source  coal can be mined from the earth & coal is a kind of energy source -> coal can be mined from the earth and used as an energy source