Populate values of text boxes depending on the choice of a drop down menu

Hello all,

I have 2 textboxes (T1 and T2) where values will be predefined in advance by reader. Is there any way to populate values of T1 and T2 depending on choice of a dropdown menu  to textbox T3? That means if reader chooses value T1 in dropbox menu , then value of textbox T1 should be populated in textbox T3  and vice versa.

thanks in advance for your comments and ideas.

Depending of dopbox menu choice, copy textfields values to another textbox