熔透角焊缝的符号，下列何种标注方式是正确的?

• A.<img src="https://timg.fentiku.com/101/2016/10/21/vMVJHAB80s.png" title='vMVJHAB80s.png' alt='vMVJHAB80s.png'/>
• B.<img src="https://timg.fentiku.com/101/2016/10/21/pMfUUXolM0.png" title='pMfUUXolM0.png' alt='pMfUUXolM0.png'/>
• C.<img src="https://timg.fentiku.com/101/2016/10/21/d253RvOXkS.png" title='d253RvOXkS.png' alt='d253RvOXkS.png'/>
• D.<img src="https://timg.fentiku.com/101/2016/10/21/qslSTmvfli.png" title='qslSTmvfli.png' alt='qslSTmvfli.png'/>

正确答案：B