We used to have a discussion, ___?

Since it will take years to know the effect of genetically modified food, it’s more sensible to give it a second thought before we eat it,        it?

It’s the third time that Li Ming has been to Xi’an , _______? 

 --Look at the photo , is this Gina’s mother?--Yes, _______.

—_____ do you go to the school library?        —Once a week.