This indicates that the BankAccount class is an abstract class and the withdrawal method is an abstract operation.

这表示，BankAccount 类是一个抽象类，而withdrawal方法是抽象的操作。

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With typical use, about 27 percent of women who use the withdrawal method experience an unintended pregnancy within the first year of use (4 percent with perfect use).

用典型使用的方法，大约有27%的有过撤回方法经历的女性在第一年的使用中意外怀孕(而完美使用的这一比例为4%)。

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The retirement income strategies financial professionals structure for investors whether they use a bucket strategy, a systematic withdrawal strategy or some other method must be based on individual investor needs and risk tolerances.

FORBES: A Bucket Strategy For Retirement Income