Mi sobrina y yo tenemos una buena
(blank), somos muy buenas amigas.

"mi sobrina y yo tenemos una buena relacion, somos muy buenas amigas"

Explanation: Ok, the sentence "Mi sobrina y yo tenemos una buena

, somos muy buenas amigas." say something like "My niece and I have a very good , we are very good friends"

And we want to complete the blank, but here we do not have any context, so we can complete the blank with any word that makes sense.

For example, we could complete it with "relation" which in Spanish is "relacion", or with "friendship" which in Spanish is "amistad".

if we choose, for example, relation, we get:

"My niece and I have a very good relation, we are very good friends"

or in Spanish:

"mi sobrina y yo tenemos una buena relacion, somos muy buenas amigas"

they need to keep water moving over their gills so they seem to have active periods and restful periods instead of undergoing deep  sleep.  they sleep swim

explanation: