The too short young man can't join the police
(If)

Rana is the best girl in the class
(good)

if the young man were tall he would join the police
if the young man wasnt too short, he would join the police
no girls is as good as rana in the class

If the young man were tall he would join the police
no girl is as good as rana in the class

If the young man weren't too short, he would join the police(الحالة الشرطية الثانية / نحول الاثبات إلى نفى والعكس) .
No girl in the class is as good as Rana.