1.ongoing a．進行中的，不間斷的(continuing)

例：They highlight her ongoing efforts to reform sanitary conditions after the war.

2.onset n．發作．（突然）開始（beginning start）

分拆記憶：on+set(放)--放在…上--發作，開始

例：I knew my sneezing was the onset of a major cold.，，at the very onset剛一開始

3.opaque a．不透明的(not transparent)；難懂的(obscure)

詞根記憶：opa(不透明)+que--不透明的

例：The room was dark because all of the windows were opaque.// I couldn't understand my professor's opaque lecture.

4.operagoer n.經常看歌劇的人(a person who frequently goes to operas)

分拆記憶：opera(歌劇)+goer(帝去的人)--經常看歌劇的人

例：Just as reading Samuel Pepys's diary gives a student a sense of the seventeenth century-of its texture and psyche-so listening to Jane Freed's guileless child narrator takes the operagoer inside turn-of-the-century Vienna.

5.optical a．眼的，視覺的(visual)；光學的(of or relating to optics)

詞根記憶：optic(眼的)+al--眼的，視覺的

例：optical illusion //an optical instrument光學儀器

6.optimal a．最佳的(best);n．最大限度(top)

詞根記憶：optim(最好)+al--最佳的

例：This is the optima/time for harvesting apples.

7.optimism n．樂觀，樂觀主義(a tendency to expect the best possible outcome or dwell on the most hopeful aspects of a situation)

詞根記憶：optim(最好)+ism--認為自己是最好的--樂觀，樂觀主義

注意：pessimism(n．悲觀，悲觀主義)

例：Increasing commercial activity would create a mood of optimism about national prosperity.

派生詞：optimistic(a．樂觀主義的)i optimistically( ad.樂觀地)

8.optimum a．最好的，最有利的（most favorable or advantageous）

詞根記憶：optim(最好)+um--最好的

例：I raised my exotic plants under optimum conditions.