( It ( ( ( is always ) ( formed ( by ( ( ( at least ) two ) substances ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ is) (ADVP (RB always)) (VP (VBN formed) (PP (IN by) (NP (QP (IN at) (JJS least) (CD two)) (NNS substances))))) (. .)))
It is always formed by at least two substances.
(ROOT (S (NP (DT All) (NNS solutions)) (VP (VBP contain) (NP (QP (IN at) (JJS least) (CD two)) (NNS substances))) (. .)))