As the lead pilot explained, I reverted to the Russian threat.
( ( As ( ( the ( lead pilot ) ) explained ) ) ( , ( I ( ( reverted ( to ( the ( Russian threat ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN As) (NP (NP (DT the) (JJ lead) (NN pilot)) (VP (VBN explained)))) (, ,) (NP (PRP I)) (VP (VBN reverted) (PP (TO to) (NP (DT the) (JJ Russian) (NN threat)))) (. .)))
I didn't know which threat to pursue.
( I ( ( ( did n't ) ( know ( ( which threat ) ( to pursue ) ) ) ) . ) )
(ROOT (S (NP (PRP I)) (VP (VBD did) (RB n't) (VP (VB know) (SBAR (WHNP (WDT which) (NN threat)) (S (VP (TO to) (VP (VB pursue))))))) (. .)))