Szia! Amelyik hosszabb ideig tart, az folyamatos múlt (was/were+ige+-ing), amelyik kevesebb, az ovis egyszerű múlt (ige 2. alakja).
Például: Miközben olvastam, ő megérkezett.
While I was reading, he arrived. (Olvasni több ideig szoktak olvasni (folyamatban van a múlt egy adott részén), míg a megérkezés az csak pár pillanat.)

1. Penicillin was invented after Alexander Fleming noticed something strange while he was observing the growth of mould near bacteria.

2. Matches were invented by John Walker, who was stirring chemicals, when the stick he was stirring with suddenly caught fire.

3. Tea was invented by Shen Nong, who smelt something nice while he was watching his servants boil water.

4. Coca-Cola was invented by John Pemberton, who combined two ingredients while he was searching for a medical cure.

5. Crisps were invented by George Crum, who was working as a chef, after a customer's complaint about their meal caused him to prepare potatoes in a different way.