(S (S (S (BASENP (DT The) (NN drug) (NN resistance)) (VP (VBZ appears) (S (VP (TO to) (VP (VB be) (VP (VBN limited) (PP (TO to) (NP (BASENP (DT the) (NNP H1N1) (NN variant)) (SBAR (WHNP (WDT which)) (S (VP (VBZ causes) (BASENP (JJ seasonal) (NN flu))))))))))))) (COMMA ,) (SBAR (IN while) (S (NP (NP (NP (BASENP (NNP H3N2)) (CC or) (BASENP (NN influenza) (NN B))) (NNS strains)) (CC and) (NP (BASENP (DT the) (NNP H5N1) (NN strain)) (SBAR (WHNP (WP that)) (S (VP (VBZ causes) (BASENP (NN bird) (NN flu))))))) (VP (VP (VBD did) (RB not)) (VP (VB show) (BASENP (JJ increased) (NN resistance))))))) (PERIOD .))