The difficulty is that a dark object strongly absorbs light and will appear to be deeper than it really is.
(it; really is; ) (The difficulty; is; that a dark object strongly absorbs light and will appear to be deeper) Context(The difficulty is,List([0, 17))):(a dark object; strongly absorbs; light)
The difficulty is,List([0, 17))
it The difficulty a dark object
really is is strongly absorbs
that a dark object strongly absorbs light and will appear to be deeper
light