Hi! Can you please tell me which sentence of each pair sounds more natural, or if there are even more natural alternatives? Thank you very much!
When I was working on my master's degree, I visited a lot of cities.
While I was working on my master's degree, I visited a lot of cities.
When I'm working on my Ph.D., I'm going to visit a lot of countries.
While I'm working on my Ph.D., I'm going to visit a lot of countries.