Guards would regulate those who entered and departed.
( Guards ( ( would ( regulate ( those ( who ( ( entered and ) departed ) ) ) ) ) . ) )
(ROOT (S (NP (NNPS Guards)) (VP (MD would) (VP (VB regulate) (NP (NP (DT those)) (SBAR (WHNP (WP who)) (S (VP (VP (VBD entered)) (CC and) (VP (VBD departed)))))))) (. .)))
Guards let people come and go freely.
( Guards ( ( let ( people ( ( come and ) ( go freely ) ) ) ) . ) )
(ROOT (S (NP (NNPS Guards)) (VP (VBP let) (S (NP (NNS people)) (VP (VP (VB come)) (CC and) (VP (VB go) (ADVP (RB freely)))))) (. .)))