EXERCISE 3I. CHỌN TỪ/ CỤM TỪ THÍCH HỢP (ỨNG VỚI A, B, C, D) ĐỂ HÒAN TH...

45. A. in B. when C. while D. duringRead the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions from 46 to 50 The forests of the tropics produce a magnificent growth of trees, but commerciallumbering is inhibited by problems that increase the cost of removal. The proliferation ofspecies that is common to all tropical forests creates difficulties because many species areworthless. The lumberman combs the forests, therefore, removing the valuable trees thatare convenient to waterways, and floating them downstream to a saw-mill. Unfortunately,tropical hardwoods tend to grow slowly; an area once cleared needs substantial time torecover, forcing the saw-mill to become mobile. Distance to market tends to beconsiderable, raising costs of the high costs associated with production. Other trees areleft untouched.