开球难度较大时，选择一根用起来能不给你添乱的高尔夫球杆。
With a difficult tee shot, select a club which will keep you short of the trouble.
净化的第一步难度较大，需要经过几年的练习来达到。
These first steps are very difficult and require many years of practice.
适用于某些密集型养猪场，这些猪场转变模式难度较大。
Suited to some pig-dense industries where resistance to change may be high.
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