But just try that (One Session Bean extending another Session Bean) and to your surprise, you will see that JBoss allows that. I remember coming across such a situation once. But in any case, go by the Specs which are the Bible!
SCJP 1.4, SCWCD 1.4 - Hints for you, Certified Scrum Master
Did a rm -R / to find out that I lost my entire Linux installation!