It's interesting that Richard and Jerry have presented different versions of what is correct here. I think they are both right! Kis is also correct in noticing that people who speak British English use the present perfect in some cases where people who speak American English use the simple past, even with "just."
means ˜a moment ago,' past and present perfect tenses are both possible in British English. A present perfect is preferred when we are giving news. Compare:Where's Eric? – He's just gone out.
I've just had a brilliant idea.
John just phoned. His wife's had a baby.
The news is the baby, not the phone call.)
In American English, a past tense is normal in all cases.Where's Eric? – He just went out.
I just had a brilliant idea.
According to Swan's explanation, since Speaker B is not giving news but is, instead, responding to a question, it seems that the past might be used even in England.
A: Have you seen Jane today?
B: I _____ her in the hallway.
A: When was that? I need to talk to her.
B: About half an hour ago, I think.
However, the tense distinction here is really not clear. I think either the present perfect or the past could be used here. Where is this question from, anyway? I'd like to see the explanation for the answer to this question.
The present tense vs. the simple past tense is one of the most popular subjects on the Grammar Exchange. Here are 14 threads: https://thegrammarexchange.infopop.cc/eve/forums?a=searc...orum_scope=340600179
*Practical English Usage, Third Edition, by Michael Swan. Oxford. 2005