题目

The forests of the tropics produce a magnificent growth of trees,but commercial lumbering is inhibited by problems that increase the cost of removal.The proliferation of species that is common to all tropical forests creates difficulties because many species are worthless.The lumberman combs the forest,therefore,removing the valuable trees that are convenient to waterways,and floating them downstream to a sawmill.Unfortunately,tropical hardwoods tend to grow slowly; an area once cleared needs substantial time to recover,forcing the sawmills to become mobile.Distance to market tends to be considerable,raising costs of transport.Because of these difficulties,only the most valuable woods can absorb the high costs associated with production.Other trees are left untouched.
1.According to the passage,one of the problems of commercial lumbering is ____.
A:selecting valuable trees is difficult
B:many of the trees are useless for timber
C:there is little variety in the types o

提问时间：2020-07-25

答案

C
A
D
D
D