http://www.english-grammar-lessons.com/presentperfectorpastsimple/menu.php
(Scroll down for the links to the exercises.)

http://www.perfect-english-grammar.com/past-simple-present-perfect-1.html

http://lyricstraining.com/

The first scene is an office. It’s a friendly, relaxed workplace, there aren’t too many people there. You can see the usual office things: file cabinets, desks, computers, pens and pencils in mugs. There are mostly men, they are working at their desks, wearing quite smart clothes, shirts and ties.

Someone is eating, the others are typing, you can hear a telephone ringing.

And then suddenly someone enters the kitchen. It is very unexpected. This person does something really nasty.

The second scene is a hospital. It is a very nice and new hospital ward. Everything is clean and white. There is a very big bouquet of flowers and  there is a TV.  There are two patients in the room. One is sleeping, the other is watching TV. A beautiful nurse enters the ward with the breakfast. When she is talking to a patient when suddenly someone enters the ward. It is very unexpected. This person does something really nasty.

The third scene is the kitchen of an Italian restaurant. There are cookers and cooks everywhere. One of them is making pizza. They are very busy, everyone is working.

And then suddenly someone enters the kitchen. It is very unexpected. This person does something really nasty.

The fourth scene is a supermarket. There is a daddy and his son in front of the dairy fridge, it's full of yoghurt, milk, cheese, cottage cheese and all the other things. Both daddy and the boy are quite well-built, they are not too cheerful. The boy wants to buy something but his daddy says no.

And then suddenly someone enters the office. It is very unexpected. This person does something really nasty.

http://knowyourmeme.com/memes/never-say-no-to-panda