The forests of the tropics produce a magnificent growth of trees,but commercial lumbering is inhibited by problems that

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 of trees in the forests
D:very few hardwoods grow in the forests
2.The lumbermen search the forests for valuable trees and choose the ones that ____.
A:are near to rivers
B:mature very slowly
C:are tropical species
D:are easy to cut down
3.According to the passage,the sawmills have to be mobile because they are ____.
A:transported near the markets
B:floated up the rivers
C:used to transport wood
D:moved away from cleared areas
4.According to the passage,relatively few trees are removed from the forests because ____.
A:the proliferation of species cannot absorb the high costs
B:the tropical hardwoods are expensive to produce
C:it is too expensive to transport the hardwoods
D:only the most valuable justify the cost
5.What can be assumed from the information given in the passage?
A:tropical forests produce too many trees.
B:too many species grow in the forests.
C:not enough species grow near the rivers.
D:useful species do not reproduce quickly.