"You and I go."
Translation:Sie und ich gehen.
That should also work, but Duolingo's algorithms skipped over it when generating the sentence for some reason. You can report such mistakes during the lesson to bring them to the attention of the course maintainers (the comments here are just for advice from other users).
There are three possibilities for this sentence, because German has three kinds of "you":
du und ich gehen - talking to one person, informally
ihr und ich gehen - talking to more than one person, informally
Sie und ich gehen - talking to any number of people, formally
This sentence doesn't use sie (she; they); it uses Sie (you).
- du is used when you are speaking to one person whom you know well.
- ihr is used when you are speaking to several people whom you know well.
- Sie is used when you are speaking to one or more people whom you do not know well
At the beginning of a sentence, you can't tell the difference between sie and Sie.
So what is used when you talk to one person you dont know well?
Sie - like English "you" - does not distinguish between talking to one person or to several people.
Herr Müller, gehen Sie schon? Mr Müller, are you going already?
Frau Schmidt, Frau Schulze und Frau Meyer, gehen Sie schon? Mrs Schmidt, Mrs Schulze, and Mrs Meyer, are you (all) going already?
It would seem to be a serious criticism of the course that no mention has been made before now of the formal second person. I am told that although the use of the familiar form "du" has increased greatly in recent years, the use of "Sie" = "you" has by no means died out, particularly among the older generation. Interestingly a similar situation seems to exist in Greek, the Duolingo course I have recently finished. In this the formal second person does not figure at all although an elderly Athenian educated friend of mine is still very reluctant to abandon it. Perhaps it is a Duolingo policy to try to stamp out formality!
There's a similar polite form for "you" in Italian and Russian as well. Although the use of the familiar form has increased, it sounds kinda rude to use it in non-familiar contexts (e.g. when you ask for information, when you talk to someone you don't know, even when you ask for a cheesburger at McDonalds etc.). I guess it's hard to understand for English native speakers, but if you have to talk to a German speaker and aren't sure what to use, I'd go for the Sie form!
It is not singular in English. Consider the progressive form "you and I are going" (plural verb) and NOT "you and I is going" (singular verb).
When the subject of the verb is a group, then the verb must be in plural form, although that may not be noticeable in the simple tenses. We would use the singular only if we repeated the verb, as in "He is going and I am going".