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Which of the following statements is false?

a. Prior to Java SE 8, it was common to associate with an interface a class containing static helper methods for working with objects that implemented the interface. b. Class Collections contains many static helper methods for working with objects that implement interfaces Collection, List, Set and more. c. Collections method sort can sort objects of any class that implements interface List. d. With non-static interface methods, helper methods can now be declared directly in interfaces rather than in separate classes.

How similar a pixel color must be to another for erasure is called ____________________.

Fill in the blank(s) with the appropriate word(s).