1.ongoing a．进行中的，不间断的(continuing)

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

2.onset n．发作．（突然）开始（beginning start）

分拆记忆：on+set(放)--放在…上--发作，开始

例：I knew my sneezing was the onset of a major cold.，，at the very onset刚一开始

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

词根记忆：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.经常看歌剧的人(a person who frequently goes to operas)

分拆记忆：opera(歌剧)+goer(帝去的人)--经常看歌剧的人

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，视觉的(visual)；光学的(of or relating to optics)

词根记忆：optic(眼的)+al--眼的，视觉的

例：optical illusion //an optical instrument光学仪器

6.optimal a．最佳的(best);n．最大限度(top)

词根记忆：optim(最好)+al--最佳的

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

7.optimism n．乐观，乐观主义(a tendency to expect the best possible outcome or dwell on the most hopeful aspects of a situation)

词根记忆：optim(最好)+ism--认为自己是最好的--乐观，乐观主义

注意：pessimism(n．悲观，悲观主义)

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

派生词：optimistic(a．乐观主义的)i optimistically( ad.乐观地)

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

词根记忆：optim(最好)+um--最好的

例：I raised my exotic plants under optimum conditions.