sentences: rock is a kind of material & rock is hard ->  rock is a hard material  rock is a hard material & granite is a hard material ->  granite is a kind of rock  granite is a kind of rock & granite forms from cooling magma ->  granite is a kind of rock that forms from cooling magma  igneous rock is a kind of rock & igneous rocks are formed by magma cooling ->  igneous rock is a kind of rock that is formed from magma cooling  granite is a kind of rock that forms from cooling magma & igneous rock is a kind of rock that is formed from magma cooling -> granite is a kind of igneous rock