Hello. I've given this question a bash. Would you agree? Do you have any other comments? I have no problem spotting the difference, but explaining it to a second language speaker can be challenging, and I was wondering if you had any experience trying to explain these kinds of sentences.
Briefly explain the differences in meaning between the following words or phrases and say how you would explain these differences to students.
a. “When I arrived the film started.” and “When I arrived the film had started.”
-- In the first sentence, you are saying that the film started at the time you arrived, but in the second sentence you are saying that the film had already started when you arrived. (I don't know if this would make things clearer for a 2nd language speaker, since I'm basically just re-phrasing the words, and using the same words they may have trouble with, like "had"...)
b. “The plane took off at 19h00.” and “The teacher took off marks for spelling and punctuation.”
In the first sentence, "took off" means that the plane lifted into the air (you might want to demonstrate this with gestures.) It is a phrase we often use when describing the motion of planes. In the second sentence, "took off" could be replaced with the word "deducted" or subtracted. In this context, it means something very different to when we talk about planes.
Your explanations hit the spot. With “When I arrived the film started", it might make more sense if you used 'then' as the arrival is before the start opf the film, no matter how short the time.