TOEFL Listening: TPO-TOEFL阅读TPO - 3171O51Q362P7QZHN$

According to paragraph 6, the construction of booms benefited the logging industry by A. reducing the pressures placed on the northern Midwest pinelands in the 1860s B. reducing the length of the downstream trip to a mill by as much as 10 miles C. increasing the number of logs that could be floated down a river at a single time D. allowing logs to move downstream more quickly and easily