Complex sentence: The acrylic block had originally been commissioned by Stanley Kubrick as the alien monolith in the film "2001-A Space Odyssey", but Kubrick rejected it in favour of a piece made from black basalt.
Split into simpler sentences: The acrylic block had originally been commissioned by Stanley Kubrick as the alien monolith in the film "2001-A Space Odyssey". However, Kubrick rejected it in favour of a piece made from black basalt.