Prétérit en -ING

What were the people doing when the plane crashed on the World Trade Center ?

   The pupils were answering the teacher's question at school.

   Some people were singing Gospel in a church in Harlem.

  A boy was playing baseball.

 Now, that you remember what we talked about in class, you can start by watching the video and doing the easy exercise here : link

 read the lesson here : link (do the exercise as well)

Then, read this link (don't forget the exercise)

Finally, make sure you know everything here : link

Last but not least, read this great summary and try to do the final exercise : link