Which tense I have to use?

[20millionmilestohope]

Hey everyone,

I have some problems with using the right tenses.
10. Do you like to have something to eat? No thank you I ... (just have) dinner.

I would fill "just had" in the gap but it says that it's wrong. Which tense would be right?

[tiorthan]

Which tense do I have to use?

10. Do you like to have something to eat? No thank you I ... (just have) dinner.

I would fill "just had" in the gap but it says that it's wrong. Which tense would be right?

The correct choice is "have just had" (Presen perfect).

Why? You're being asked whether you want somthing to eat? That's a question about the present. Your answer gives a reason why you don't want anything right now. The reason is a direct (that's why you use "just") result of some action you did in the past.
Since you're talking about now: The time is non-past (aka. present).
Since you're talking about a direct result of an action: The aspect is perfect.
= Present perfect.

[20millionmilestohope]

Thank you for the explanation. I found the following sentence on an other website:

"When she went out to play, she ...
(do / already)
her homework."

"..., she had already done ..." is right, isnt it? But why "When she WENT out to play" and not "When she was going out to play"? I thought "When" is a signal word for Past Progressive?

[tiorthan]

Generally, a signal word is just a pointer to a possibility. It doesn't enforce anything. If you come across a signal word all you should do is think about whether the signalled grammatical feature is actually useful or necessary. (Some signal words actually enforce the related grammatical form, but most don't.)

The past progressive is a past with a progressive aspect (who'd though that). Progressive aspect means, that you are putting emphasize on the duration of the action. But emphasize on the duration is only necessary when things happen simultaneously or when there is a period of time involved or when the speaker wants to emphasize the duration. Neither applies here because "homework" and "go out to play" happen in sequence and when is used to identify a point in time in this sentence. I also see no point in emphasizing duration so consequently, a progressive is not necessary and you never use an unnecessary aspect.

[nrjones]

Hey everyone,

I have some problems with using the right tenses. I found a website where I can practise using the right tenses
10. Do you like to have something to eat? No thank you I ... (just have) dinner.

I would fill "just had" in the gap but it says that it's wrong. Which tense would be right?

In American English, one would say "No thank you, I just had dinner." So you're right.

Thank you for the explanation. I found the following sentence on an other website:

"When she went out to play, she ...
(do / already)
her homework."

"..., she had already done ..." is right, isnt it? But why "When she WENT out to play" and not "When she was going out to play"? I thought "When" is a signal word for Past Progressive?

"When" is not a signifier of past progressive and "When she went out to play" is correct. This is just one example of when simple past is used. I think you may be confusing "when" with "while" because in German, you'd use "als", which can mean either.