Que : Why are you late ?
Ans a) : I was stuck in traffic.
Ans b) : I stuck in traffic.
Which sentence should I use ? Simple past tense or Passive voice?
I want to refer past event and both sentences are referring to past event.
Meaning ,
a) I am late because I was stuck in the traffic.
b) I am late because I Stuck in the traffic.
Similarly,
a) Two persons were killed in accident.
b) Two persons killed in accident.
Is there any rule to omit or include was / were the English?
The idiom is to be stuck in traffic meaning to be caught in a traffic jam:
I was stuck in traffic
where stuck is the adjective meaning unable to move, or set in a particular position, place, or way of thinking.
As for
Two people killed in accident
it is sooner a headline than a stand-alone sentence:
Two people were killed in an accident.
Taking your second example first, "were" is necessary. (b) sounds like a newspaper headline; it is a grammatically incorrect abbreviation. It would not be understood unless it was a newspaper headline. "To kill" ≠ "to die"; sentence (b) literally means that two people committed murder. This is why "were" is necessary - it turns "persons" from the subject of the sentence into the object of the sentence.
The full sentence should read "two persons were killed in an accident" or "two persons were killed in the accident" or "two people were killed in the accident".
For your first example, both answers are technically correct. However, it is unusual to say that a person "stuck" - the active, intransitive verb "stick" is normally for inanimate subjects, and only inanimate subjects.
"I was stuck in traffic" sounds good - "stuck" is an adjective, here.
