This is quirky enough that I suspect it's homework, though you did not tag it as such. And since we're not supposed to do your homework for you (so you don't get into cheating trouble with your institution/teacher) I suggest you just look at my solution to your other, very similar question here : Click here
Then figure out how to modify only the odd numbered indexes. Hint:
for k = 1 : 2 : length(words) % Loop to do words 1, 3, 5, etc.