AnonymousIf you were to choose the correct verb form in bold, which one would you bet on, and why?
To me, the most idiomatic choices are
Why didn't you tell ...? and
I tripped over it just now. It's a case of a sudden action or event in the very recent past -- not a matter of a history of experiences, as in
I have tripped over that board at least a dozen times this week or
If I've told you once, I've told you a thousand times to be careful about that board. Compare:
I just saw that film last night. (relating my action) vs. I've already seen that film several times. (relating my history)
I ran into an old friend at the grocery store today. (action) vs. I've often run into friends at the theatre. (history)
Did you see that man steal the shirt? It happened just now! (action) vs. Have you ever seen anyone steal a shirt? It has happened in this store more than once. (history)
_____
The present perfect cannot be used with a phrase indicating "definite time". just now often qualifies as a "definite time".
CJ