Get Your Thinking Caps On

From the Mensa Puzzler Calendar.

Find the word that best completes the following sequence.

NINE EIGHT TEN NINETEEN

a) SEVEN
b) TWENTY
c) NINETY

Did I get this? Pfft! No!

ANSWER
Mark Mossa emailed me the answer about 30 seconds after I posted this so I'll go ahead and put it up now...

c) NINETY (each word starts with the last letter of the preceding word).