html - How to generate an event when an item on a drop down list is highlighted with the mouse -

i know how generate event item on drop down list highlighted mouse. here code example:

<select>   <option value="a">a</option>   <option value="b">b</option>   <option value="c">c</option>   <option value="d">d</option> </select> 

i tried following without luck...

<select>   <option onmouseover="myfunction()" value="a">a</option>   <option onmouseover="myfunctiontwo()" value="b">b</option>   <option onmouseover="myfunctionthree()" value="c">c</option>   <option onmouseover="myfunctionfour()" value="d>d</option> </select> 

i new html please gentle suggestions. came across challenge preparing myself big.

thanks.