1.observatory n．天文台(a building ,a place, or an institution designed and equipped for making observations of astronomical, meteorological, or other natural phenomena)

词根记忆：来自observe(v.观察)

例：Astronomers at the Palomar Observatory have discovered a distant supernova explosion.

2.obsess v.（使）困扰，（使）着迷( to haunt or excessively preoccupy the mind of)

词根记忆：ob+sess(=sit坐)--坐着不走--（使）困扰，（使）着迷

例：The fear of death obsessed her throughout her old age.

派生词：obsession(n.迷住：萦绕)

3.obsolescence n．荒废；过时( the condition of being nearly obsolete)

词根记忆：来自obsolete(a.废弃的)

例：technical obsolescence技术过时

4.obstacle n.障碍(something that impedes progress or achievement)

词根记忆：ob（反）+st(=stand站)+acle（东西）--反着站的东西--障碍

例：In the speaking contest, Randolph faced formidable obstacles.

5.occupation n．工作，职业(a job; employment);占领(the act or process of taking possession of a place or area)

词根记忆：来自occupy(v.占领；使用)

例：There is no occupation for which the risk of developing an animal- induced allergy is higher than 30 percent.

派生词：occupational(a．职业的；占领的)

同根词：preoccupation(n．全神贯注，入神)

6.occupational a．职业的（of the activit3t in which one engages）；占领的(taking possession of a place or area)

词根记忆：来自occupation（n．职业：占领）

例：Unlike men of science; women of science have had to work against the grain of occupational stereotyping to enter a "man's world".

同根词：preoccupation(n．全神贯注；当务之急)

7.occurrence n.发生(the action or instance of occurring)；事件(sth. that occurs)

词根记忆：oc(加强)+curr(发生)+ence--发生

例:It provides an explanation for the occurrence of a situation described in the first paragraph.

同根词：concur(v.同时发生)

8.odd a．奇怪的(peculiar)；奇数的(impar);n.[pl.]可能性(possibility)；不平等(imparity)

联想记忆：奇奇(odd)相加(add)为偶

例：I avoided the odd person who was talking to himself.//The odds are 10 t0 1 against your winning.//against odds尽管有极大的困难//at odds争执，不一致

派生词：oddity(n.奇特的人或物：古怪的性质)

9.odometer n.（汽车）里程表（an instrument for measuring the distance traveled as by a vehicle）

词根记忆：odo(旅行)+meter(测量)--测量旅行的东西--里程表

例：I couldn't determine how far l'd driven because my car's odometer is broken.