Ответ:

1. I have already seen a flashmob / I haven't seen a falshmob yet.

3. 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.

Объяснение:

Элементарная грамматика, учите конструкции постороения предложений в Present Perfect, сможете сами в будущем сделать,