Which statement is false?

All built-in collections are synchronized.
b. Concurrent access to a Collection by multiple threads could cause indeterminate results or fatal errors.
c. To prevent potential threading problems, synchronization wrappers are used around collection classes that might be accessed by multiple threads.
d. A synchronization wrapper class receives method calls, adds some functionality for thread safety and then delegates the calls to the wrapped class.

a. All built-in collections are synchronized. Actually, most built-in collections are unsynchronized by default for performance reasons.