36.It can be inferred from paragraph 2that previous generations of foresters

(A)did not study the effects of alders on forests

(B)did not want alders In forests

(C)harvested alders for lumber

(D)used alders to control the growth of evergreens

37.The word "they"in line 21refers to

(A)newly developing soils

(B)alders

(C)bags

(D)chemical changes

38.According to the passage that alders are used in mountainous areas to

(A)nitrogen

(B)calcium

(C)carbon

(D)oxygen

39.It can be Inferred from the passage that alders are used in mountainous areas to

(A)prevent water from carrying away soil

(B)hold the snow

(C)protect mines

(D)provide material for housing

40.What is the author's main purpose in the passage?

(A)To argue that alder trees are useful in forest management

(B)To explain the life cycle of alder trees

(C)To criticize the way alders take over and eliminate forests

(D)To illustrate how alder trees control soil erosion