Learn vocabulary and give rice

I just came across this awesome vocabulary game called FreeRice. The game is simple, you are given a word and a choice of four words from which you must pick the best synonym. If you choose the correct answer your vocabulary level goes up (max is 50) and the site donates 50 grains of rice to the United Nations. An incorrect answer resets your level to 1, but you do learn the correct answer. I've made it to level 43 a couple of times but the words start to get really esoteric at that point and I'm basically just guessing.