as the rate of rocks cooling decreases , the crystal size of the rock will increase & rate is a kind of measurement of speed ->  as the speed of rocks cooling decreases, the crystal size of the rock will increase  as the speed of rocks cooling decreases, the crystal size of the rock will increase & to slow / to slow down decreases speed ->  a rock cooling slowly causes the crystal size of the rock to increase  a rock cooling slowly causes the crystal size of the rock to increase & if something causes something else then that something affects that something else ->  a rock cooling slowly affects the crystal size of the rock  a rock cooling slowly affects the crystal size of the rock & if something affects something else then that something else indicates whether that something happened ->  the crystal size of a rock indicates whether the rock cooled slowly  the crystal size of a rock indicates whether the rock cooled slowly & crystal size is a property of rocks and includes values of small / large -> crystal size is a property of a rock that indicates whether a rock cooled slowly