A Korean survey shows that shopping cart handles are the most bacteria-carrying items among some ________used objects.

Nancy reminded me of what I should ________ have forgotten.

—Do you think our teacher is　　　　？—Yes， he always corrects our homework and prepares his lessons　　　　. 

 ---I was riding along the street and all of a sudden, a car cut in and knocked me down. ---You can never be         careful in the street.

In my opinion, she is too young to take care of the pet dog ______.