在定于从句中,当先行词前面有:1.thesame/thevery/theonly/thelast修饰时比用that.
2.当主句以Therebe/Herebe开头时必用that.
3.当先行词是形容词或最高级,或被形容词、最高就修饰必用that.
4.先行词是much/all/little/few/none/something/anything/nothing/somebodyect.必用that.
5.当主句是以who/which开头的特殊疑问句时比用that.
你说的情况是否用that与just本身没关系,记住:学语言要灵活,不要像背公式一样,要视语法和语境来定.