According to the grammar rules for verb tenses. Choose the best alternative to fill the blanks:

1- The police ______________________ (arrest) the suspects last night.

2- They ___________________________ (not/steal) anyone for a month.

3- Scientists ________________________ (test) new medicine last year.

4- I ____________________________ (Not/find) my keys since you left.

5- They _________________________ (work) a lot last night