在结构图中，安装螺栓表示方法，下列哪一种形式正确?

• A.<img src="https://timg.fentiku.com/101/2016/10/21/rt7UXdhVV4.png" title='rt7UXdhVV4.png' alt='rt7UXdhVV4.png'/>
• B.<img src="https://timg.fentiku.com/101/2016/10/21/gPI6RoWTLo.png" title='gPI6RoWTLo.png' alt='gPI6RoWTLo.png'/>
• C.<img src="https://timg.fentiku.com/101/2016/10/21/IR3QU6pzFg.png" title='IR3QU6pzFg.png' alt='IR3QU6pzFg.png'/>
• D.<img src="https://timg.fentiku.com/101/2016/10/21/BuwF7OYMa3.png" title='BuwF7OYMa3.png' alt='BuwF7OYMa3.png'/>

正确答案：C