How does wca4z support a strategy where only selected COBOL programs are transformed while the rest remain in COBOL?

Think of it like working hands-on with IBM mainframe systems — the answer here is 'By requiring all programs in an application to be transformed simultaneously in one batch'. wca4z generates adapter code that allows newly produced Java modules to call or be called by unchanged COBOL programs, enabling incremental adoption without a big-bang cutover. On real mainframe exams, this concept comes up repeatedly so make sure you have it locked in.