Which set of signs $$+$$ and $$-$$ needs to be placed in the boxes to make the expression true?  $$4\square 3\square 2\square 1=8$$ 
选项为:A:$$+$$, $$-$$, $$+$$  B:$$-$$, $$+$$, $$-$$  C:$$+$$, $$+$$, $$-$$  D:$$+$$, $$+$$, $$+$$  E:$$-$$, $$+$$, $$+$$  请回答其中一个选项.