feasible : 指完全可行，切实可行，强调成功的较大可能性。
- With the extra resources, the project now seems feasible.
- It may be feasible to clone human beings, but is it ethical?
possible : 多用来消除对某事的怀疑，侧重从客观上看有存在或发生的可能。
- I can't get it all done by Friday - it's just not possible.
- Is it possible to buy tickets in advance?
- They got as far as was humanly possible (= as far as anyone could have) before turning back.
practicable : 强调经过证明是有效的，合乎实际，行得通的。
- The troops will be brought home as soon as practicable.
- It is not practicable to complete the tunnel before the end of the year.