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 forests, therefore, removing the valuable 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 with production. Other trees are left untouched. 1. What is the main topic of the passage? A. The growth rate of hardwoods B. The transportation difficulties C. The number of useless trees D. The high costs of commercial lumbering in the tropics. 2. The word “valuable” in line 4 means­­­­­­­­­­­­­­­­­­­­­_____________ A. precious B. important C. major D. useless