(S (S (S (NP (BASENP (NNS Roads)) (PP (IN in) (BASENP (NNP Afghanistan)))) (VP (VP (VBP are) (ADVP (RB often))) (ADJP (JJ difficult) (SBAR (S (VP (TO to) (VP (VB traverse)))))))) (COMMA ,) (S (ADVP (RB so)) (S (BASENP (NNS militaries)) (VP (ADVP (RB often)) (VP (VP (VP (VBP contract) (BASENP (NN aircraft))) (PRN (COMMA ,) (PP (ADVP (RB especially)) (PP (IN from) (BASENP (NNP Russia)))) (COMMA ,))) (S (VP (TO to) (VP (VP (VB transport) (BASENP (NNS troops) (CC and) (NN cargo))) (PP (IN between) (BASENP (NNS bases))))))))))) (PERIOD .))