When provided with the single word options, "we chose" isn't an option, only "we were choosing" which is the imperfect, not preterit which is a different word. I got stumped at first, too!
1 . It's similar to how you can use either simple present or progressive in English to express the same simple present in Spanish, though the simple present is the closest translation.
I eat it. (present)
I am eating it. (present progressive)
I guess it also applies with the preterite. Please feel free to correct, anyone though.
I ate it. (preterite)
I was eating it. (preterite progressive)
2 . The simple present tense of "elegir" for the "nosotros" form is "elegimos". But its preterite tense is also "elegimos", so without context, the verb in the sentence above can be treated as either present or preterite.
Elegimos los colores juntos.
We choose the colors together. (present)
We are choosing the colors together. (present progressive)
We chose the colors together. (preterite)
We were choosing the colors together. (preterite progressive)
I also reported this, since "elegimos" is the same for present and preterite conjugations in Spanish.
I am sure "We choose the colors together." should be accepted but it won't let me report it on this item :(
To use the nosotros form of the verb to say "Let's ...", it changes to the subjunctive.
Let's choose ... Elijamos ...
Let's eat ... Comamos ...
Let's talk ... Hablemos ...