EXERCISE 3I. CHỌN TỪ/ CỤM TỪ THÍCH HỢP (ỨNG VỚI A, B, C, D) ĐỂ HỊAN 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 commercial lumbering is inhibited byproblems that increase the cost of removal. The proliferation of species that is common to all tropical forestscreates difficulties because many species are worthless. The lumberman combs the forests, therefore, removing thevaluable trees that are 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 to recover, forcing the saw-mill to become mobile. Distance to market tends to be considerable, raising costs of the high costs associated withproduction. Other trees are left untouched.