the usage of the word pop as a verb

[aleaf]

I made several sentences with the word "pop" please correct the sentences for me. Thanks~~
An advertisement popped in front of me today when I opened a website.

He popped in front of me after ten years we parted.

My boss popped in when I was chatting with my friend over telephone.
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Try to change youself before you try to change others.

[Mister Micawber]

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The first two would be make more sense with 'popped up'. 'Popped' alone usually means 'exploded'.
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Canadian-American native speaker
who teaches English for a living at Mister Micawber's
ESL cafe: Interview with Mister Micawber