blank in shell script

Try to avoid the use of blank in pathnames. It will drive you crazy under some circumstances. Take the following script as an example.

#!/bin/sh
opt="-path \"*/a bc\" -prune"
find $opt -o -print0
bash -c "find $opt -o -print0"

find $opt -o -print0 does not work. But bash -c "find $opt -o -print0" works. I have tried very hard to find a way to make the former work. But I failed. I will be happy to hear if anybody has a solution.