Introduction:
The EP tree index method is a data structure used for organizing and accessing data in a database. It is a balanced tree structure that stores records in a specific order to optimize data retrieval. In this question, we are given a series of statements about the EP tree index method and we need to identify the true statements.

Analysis:
Let's analyze each statement one by one and determine whether it is true or false.

a) Records are physically stored in primary key order.
This statement is true. In the EP tree index method, records are stored in the database in primary key order. This means that the records are physically arranged in the database file based on their primary key values. Storing records in primary key order allows for efficient retrieval of data using the EP tree index.

b) B trees use a hashing algorithm.
This statement is false. B trees do not use a hashing algorithm. B trees are a type of self-balancing search tree that is commonly used for organizing data in databases and file systems. They use a different mechanism to maintain balance and ensure efficient data retrieval. B trees use a split and merge operation to keep the tree balanced.

c) The index tree may become unbalanced as a result of updates.
This statement is true. In the EP tree index method, the index tree may become unbalanced as a result of updates. When records are inserted or deleted from the database, the index tree needs to be updated to reflect the changes. If the updates are not properly handled, the index tree may become unbalanced, which can lead to degraded performance in terms of data retrieval.

d) None of the above.
This statement is false. As discussed above, statement a is true, statement b is false, and statement c is true. Therefore, the correct answer is option 'A', which corresponds to statement a being true.

Conclusion:
In conclusion, the true statement regarding the EP tree index method is that records are physically stored in primary key order. This ensures efficient data retrieval based on the primary key values. The other statements, regarding B trees using a hashing algorithm and the index tree becoming unbalanced as a result of updates, are false.