How many countries _____ you visited so far?
How many countries have you visited so far?
Now I smoke 10 cigarettes a day, but I didn't _____ to smoke at all when I was younger.
Now I smoke 10 cigarettes a day, but I didn't use to smoke at all when I was younger.
It's only 9 am, but I _____ already had 4 cups of coffee.
It's only 9 am, but I have already had 4 cups of coffee.