Highlighing words in sentence one by one

I am making game in unity where i am having a sentence which i have to display in different forms for eg if i have a sentene "I am using Unity"

i want to display this text in textbox as:

 <b>I</b><i>am using Unity</i>
 <i>I</i><b>am</b><i>using Unity</i>
 <i>I am</i><b>using</b><i>Unity</i>
 <i>I am using</i><b>Unity</b>

This means one by one the words of the sentence should be displayed in bold and everything else in italic.

i have split the sentence in words and inserted each word in an array using

 TextArray = sentence.split(null); 

where null is the space in between the words now how should i loop through the array to create the above rich text pattern?