TOEFL Reading: ETS-TOEFL阅读机经 - 5G845E8EV733846LL$

Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information. A. Tilling by hand was so difficult that cleared land in Northern Europe was often abandoned and allowed to return to its natural forested state. B. Cleared land was probably tilled by hand, while the forests of Northern Europe were cleared only in small sections and used for short periods. C. In the vast natural forests of Northern Europe, farmers had to work the land by hand, with little direct help from animals. D. Fire enabled northern European farmers to enrich cleared land enough to cultivate their crops for short periods of time.