【单选题】
120°是多少( )弧度
①
<img class="kfformula" src="20190808/1565256897593693.png" data-latex="\frac {\pi } {6}" width="86" height="55"/>
②
<img class="kfformula" src="20190808/1565256897599656.png" data-latex="\frac {2\pi } {3}" width="87" height="63"/>
③
<img class="kfformula" src="20190808/1565256897738219.png" data-latex="\frac {\pi } {3}" width="86" height="73"/>
④
<img class="kfformula" src="20190808/1565256897259624.png" data-latex="\frac {5\pi } {6}" width="76" height="63"/>