如何使用d3更改添加到圆圈的附加文本颜色

Hi I am playing with d3 , please see the following code i used to draw circles bounded with my data and than for each circles i added text. it works fine for me however as of my requirement i want to change access this appended text e in mouseover event of circle, actually i wish to change the color of the appended text to black to show this circle is selected. the code does not give any error but also does not access the appended text as nothing happens . Any suggestionHi I am playing with d3 , please see the follow