an interesting topic , some intriguing characters 
(ROOT (NP (NP (DT an) (JJ interesting) (NN topic)) (, ,) (NP (DT some) (JJ intriguing) (NNS characters))))
(ROOT (NP (NP (DT ) (JJ ) (NN )) (, ) (NP (DT ) (JJ ) (NNS ))))