用括號中所給詞的正確形式填空（必要時可加助詞），使句子表達更準確。

1．I _________（see）Isabel in the aquarium ten minutes ago，now she _________（buy）some souvenirs．

2．They _______（take）some photos in Forbidden City if it _________（not snow）next vacation．

3．Vegetables _________（be）fresh in the market，Mrs. Black often stops _________（buy）some on her way home．

4．I _________（send）a letter to my friend Tom yesterday morning．And now I am looking forward to _________（hear）from her．

5．Keep quiet，please．The scientist _________（give）us a talk on pollutions．