46.(A)The latest practices of accurate mapmaking.

(B)The impact of epidemics on mass migration.

(C)The advantages of establishing international trade agreements.

(D)The technology used to locate the Old Canada Road.

47.(A)Watch a slide show about trees.

(B)Learn how to prevent Dutch elm disease.

(C)Study the history of the campus buildings and grounds.

(D)Look at examples of trees on campus.

48.(A)History.

(B)Physical education.

(C)Botany.

(D)Architecture.

49.(A)Its leaves are yellow.

(B)Its leaves are lopsided.

(C)It is very tall.

(D)It is not an angiosperm.

50.(A)It has grown too tall for its designated space.

(B)It may be diseased.

(C)Its branches are being broken off.

(D)It no longer hears from.