The concrete classes of the JCF that:. a. implement the Set interface all extend the AbstractMap class should be assigned.
b. the value null when they are empty collections.
c. are optimized for fast searching of elements in a collection.
d. none of these.

c. are optimized for fast searching of elements in a collection.

Explanation:

JCF is an acronym for Joint Collection Framework. It is a unified, ready-made architecture that comprises of Algorithms, Interfaces, and Classes.

This enables users or coders to write easy to formulate programs that can perform the actions of storing and processing data.

Part of the functions of JCF Classes is to execute standard undertakings like searching, sorting, and processing of data in a faster manner in a group or collection.

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