49.　　 knowledge n. – knowledgeable a.　 (*change v. – changeable a.)

48.　　 jewel n. – jewelry n. – jeweler n. – jeweled a.　

47.　　 invisible a. –visible 　[s] inaudible, inaccurate, inefficient, inconvenient 　incorrect

46.　　 interrupt v. – interruption n.　

45.　　 instruct v. – instruction n. – instructive a. – instructor n.

44.　　 innocence n. – innocent a.

43.　　 history n. – historic a.有历史意义的 – historical a.历史的（真实事件）

historic – city/ landmark/ spot/ document　　 historical event

42.　　 help v. – helpful a. (*with the help of)

41.　　 guilt n. – guilty a.　　 (*have a guilty conscience 感到内疚)

40.　　 Greek n. – Greece n.