Complex sentence: A manifold has a volume form if and only if it is orientable, and orientable manifolds have infinitely many, since multiplying a volume form by a nonvanishing function yields another volume form.
Split into simpler sentences: A manifold has a volume form if and only if it is orientable. An orientable manifold has infinitely many volume forms, since multiplying a volume form by a non-vanishing function yields another volume form.