Rule 9.4: More Prepositions - the Present Perfect Simple vs. the Present Perfect Progressive

1. Ago

We can use ago with a Past Simple verb to say when something happened. A: When did the Second World War start?
B: It started over 50 years ago.
(= it started 50 years back in the past from now.)

2. First and last

Look at these sentences, where first means “for the first time” and last means “for the last time”. Elisabetta and Fernando first met 10 years ago.
The planet Pluto was first seen in 1940.
A: When did you last visit Prague?
B: I last visited Prague two years ago.