Question: What is the effect of using the volatile keyword in Java with respect to variables?

A) It ensures that changes to a variable are immediately visible to all threads, preventing caching of the variable in thread-local memory.
B) It makes a variable constant, preventing any modifications to its value once it has been initialized.
C) It restricts the variable's access to within the class it is defined in, making it private to that class.
D) It allows a variable to be used in synchronized blocks, making it thread-safe for concurrent access.