Fill in: can/can't or could/couldn't.
When I was younger, I didn't know the first thing about computers. I 1).......... even turn it on! One day, I saw an ad about free computer courses. In no time, I 2)........ use a computer like an expert. I liked it so much that I decided to study it at university. Today, I'm a computer programmer and I 3)........... not only use it, but I actually make new programmes for it. I love computers and I 4) .......... imagine my life without them. ​