Obviously the last one is not correct but can anyone explain why…? What’s the difference between the two?
“500 were killed” is a passive voice. In other words, instead of saying “Someone killed 500 people”, you say “500 were killed”.
But, you cannot say “500 were died”. You can say “500 died” or “500 were dead”.
Kill is a verb that can be used in passive voice.
Learn English Via Listening | Beginner Level | Lesson 14 | Remembrance Day
There are some verbs that can’t be used in passive voice, and DIE is one of them.
Verbs that cannot be used with passive voice:
1) Intransitive verbs (verbs that do not take an object).
- I arrived to the train station at 16:00.
- I slept very well tonight.
2) Some state verbs (have, lack, resemble, suit, etc.)
- Jessica has three sisters.
- Does this pen belong to you?
3) Verbs that are used exclusively in the passive voice (don’t have an active form):
- He was born in July.
- The package was shipped to Jamaica.
I hope this clarifies the confusion. 🙂
P.S. There’s more information about the passive voice here:
How To Use The Passive Voice With Helpful Examples