1.extend v.延展，延长(to spread or stretch forth)

词根记忆：ex(出)+tend(伸展)--伸出去--延展

例：The installments(分期付款)will extend over a period of exactly 3 years.

派生词:extension(n.延伸;提供)；extended(a．延长的)

2.extensive a．大量的；多方面的，广泛的(having wide or considerable extent)

词根记忆：来自extend(v.延伸；推广)

例：His extensive experience in other parts of Asia helped him to overcome cuttural barriers.

派生词:extensively( ad.广阔地)

同根词：extent(n.程度;范围)

3.exterminate v.消除，消灭（to get rid of completely, usually by killing off）

词根记忆：ex（出）+termin（界限）+ate--超出生存的界限--消除

例：By the 1930's, bounty hunters had exterminated most of the gray wolves in the United States.

4.external a.外面的，表面的(outside)

词根记忆：ex(外)+ternal一外面的，表面的

例：external environment外部环境

5.extinct a．灭绝的(no longer existing)；（火山等）熄灭的(no longer active)

词根记忆：ex+tinct(促使)一使…失去--灭绝的

例：Unless tiger hunting decreases, tigers will soon be extinct in the wild.

派生词:extinction(n.消失，废止)

同根词：distinction（n.差别）：instinct(n.本能，天性)；extinguish(v.熄灭，消灭)

6.extinction n．消灭，废除(the process of eliminating or reducing a conditioned response by not reinforcing it)

词根记忆：来自extinct(v.使熄灭)

例：The extinction of the salmon populations that spawn in polluted streams is accelerated.

同根词：extinctive(a.使消灭的)

7.extinguish v.消灭(to bring to an end)；费息灭(to cause to cease burning)

联想记忆：ex（出去）+ting( =sting刺)+uish--去掉刺--熄灭

例：Arabs and Bulgarians at times threatened to take Constantinople and extinguish the empire altogether.//Most indMduals have no formal training in how to extinguish fires.