if it looks like a duck walks like a duck and quacks like a duck it must be a

*上的解释：
Operational definition中有这样一段：
if it walks like a duck and quacks like a duck,it must be some kind of duck,may be regarded as involving a sort of measurement process or set of tests (see duck test)
楼上各位对于原句的翻译都是对的,我就不再翻译了,除了这句：
may be regarded as involving a sort of measurement process or set of tests
可以被看作是涉及到一种测量过程或测试（参见duck test）
于是我转到duck test,有这样的解释：
The duck test is a humorous term for a form of inductive reasoning.
鸭子的测试是归纳推理的一种幽默的说法.
This is its usual expression:
“If it looks like a duck,swims like a duck,and quacks like a duck,then it probably is a duck.”
The test implies that a person can identify an unknown subject by observing that subject's habitual characteristics.It is sometimes used to counter abstruse arguments that something is not what it appears to be.
这个测试意味着一个人可以通过观察主体的习惯性的特点来鉴别未知主体.它有时被用来反驳“某物的实质其实并不是它表面所呈现的那样”这样一种令人费解的深奥的观点.
现在你应该理解了.不明白可以再联系我.