Verified answer

1 (+) I have already seen a flashmob.

 (-) I haven't seen a flashmob yet.

2 (+) Sam has already bought a new jacket.

 (-) Sam hasn't bought a new jacket yet.

3 (+) We have already shopped online.

 (-)  We haven't shopped online yet.

4 (+) You have already had a swimming lesson.

  (-) You haven't had a swimming lesson yet.

5 (+) Fiona and Frank have already opened an online store.

  (-) Fiona and Frank haven't opened an online store yet.

6 (+) Sally has already posted a video on YouTube.

  (-)  Sally hasn't posted a video on YouTube yet.