( ( ( ( ( ( ( There ( are ( ( no ( relevant doublet ) ) ( , ( triplet ( , ( or ( quadruplet registers ) ) ) ) ) ) ) ) , ) so ) ( ( since ( the singlet ) ) ( ( ( ( ( ( ( ( ( targets one ) , ) two ) , ) three ) , ) and ) four ) ( are ( equiprobable ( ( a ( random choice ) ) ( is made ) ) ) ) ) ) ) , ) ( ( a four ) ( in ( this case ) ) ) ) . )
(ROOT (S (S (NP (EX There)) (VP (VBP are) (UCP (NP (DT no) (JJ relevant) (NN doublet)) (, ,) (ADJP (JJ triplet)) (, ,) (CC or) (NP (NN quadruplet) (CD registers))))) (, ,) (IN so) (S (PP (IN since) (NP (DT the) (NN singlet))) (NP (NNS targets) (CD one) (, ,) (CD two) (, ,) (CD three) (, ,) (CC and) (CD four)) (VP (VBP are) (ADJP (JJ equiprobable) (SBAR (S (NP (DT a) (JJ random) (NN choice)) (VP (VBZ is) (VP (VBN made)))))))) (, ,) (S (NP (DT a) (CD four)) (PP (IN in) (NP (DT this) (NN case)))) (. .)))
There are no relevant doublet, triplet, or quadruplet registers, so since the singlet targets one, two, three, and four are equiprobable a random choice is made, a four in this case.
(ROOT (S (NP (NP (CD Four) (NNS children)) (VP (VBN born) (PP (IN at) (NP (CD one) (NN birth))))) (VP (VBP are) (VP (VBN called) (NP (NNS quadruplets)))) (. .)))