【考查知识点：函数的连续性与间断点】 函数的间断点为(     )．

<span style、"font-family: 'times new roman', times, serif;"><em>x</em>=1</span>

<span style、"font-family: 'times new roman', times, serif;"><em>x</em>=2</span>

<span style、"font-family: 'times new roman', times, serif;"><em>x</em>=3</span>

<span style、"font-family: 'times new roman', times, serif;"><em>x</em>=4</span>