JAMB Use of English 1983 Question 27

Choose the option nearest in meaning to the underlined expression: It is usually hard to change the course of action when one crosses the rubicon. The underlined expression, as used in this sentence means to

1. A.pass through a place called rubicon
2. B.cross a river called rubicon
3. C.cross a bridge called rubicon
4. D.pass a special test
5. E.be irrevocably committed.