nakunaru hazu desu ? nakunari sou desu?

From: Chan (engineer_hihi_at_yahoo.com.hk)
Date: 12/28/04 

Date: 28 Dec 2004 09:34:20 -0800

It's a JLPT-03 question...(this year)

A$B!'!V$"!"$?$$$X$s$@!#$3$N<V%,%=%j%s$,(B $B!2!2$h!#!W(B
B$B!'!VK\Ev$@!#(B $BAa$/(B $BF~$l$?$[$&$,(B $B$$$$$G$9$M!#!W(B

1) nakunaru rashii desu $B$J$/$J$k(B $B$i$7$$(B
2) nakunaru sou desu $B$J$/$J$k(B $B$=$&$G$9(B
3) nakunaru hazu desu $B$J$/$J$k(B $B$O$:$G$9(B
4) nakunari sou desu $B$J$/$J$j(B $B$=$&$G$9(B

Which one is correct?
I chose number 3 , but all my friends chose number 2...
Is number 4 the correct answer?