English grammar_ Adverb - ever / once

1> ever

Have you ever seen koala while you were in Australia？
Did you ever see a koalo while you were in Australia?
Have you ever seen a koala when you were in Australia ？

• while ： Conjunction , Then for a period of time ;
  when： Conjunction , Take the instant action ;

• ever 【adv.】 once
  In a negative or interrogative sentence , Used in the past or present perfect tense ;

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This is the saddest scence that I have ever seen.
This is the saddest scene I have ever seen .

She is the most beautiful girl that I‘ve ever seen.
She is the most beautiful girl I have ever seen .

• ever 【adv.】 once
  In the affirmative , The collocation is very advanced ;

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2> once

The house once belonged to my father.
This house used to belong to my father .

• once 【adv.】 once
  Used in affirmative sentences ;

*belong 【vi】 Add preposition to;

• transitive verb 【vt.】 transitive verb ;
  intransitive verb 【vi.】 intransitive verb ;