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

47. According to the passage, one of the problems of commercial lumbering is that ______.A. there is little variety in the types of trees in the forestsB. selecting valuable trees is difficultC. many of the trees are useless for timberD. very few hardwoods grow in the forests