( ( Have ( ( ( ( at least ) two ) layers ) ( surrounding ( the balloon ) ) ) ) . )
(ROOT (S (VP (VB Have) (NP (NP (QP (IN at) (JJS least) (CD two)) (NNS layers)) (VP (VBG surrounding) (NP (DT the) (NN balloon))))) (. .)))
Have at least two layers surrounding the balloon.
(ROOT (S (NP (NP (DT The) (NN pleura)) (SBAR (WHNP (WDT that)) (S (VP (VBZ surrounds) (NP (DT the) (NNS lungs)))))) (VP (VBZ consists) (PP (IN of) (NP (CD two) (NNS layers)))) (. .)))