Hi, YSchneider . I am not a native speaker and this is indeed a tough grammar point for non-native speakers. Here is an extract from CGEL*: Did you lock the front door? in a domestic situation where it is known that the front door is locked at

http://ccc.commnet.edu/grammar/progressive.htm #begin quote The progressive forms of a verb indicate that something is happening or was happening or will be happening. When used with the past, the progressive form shows the limited duration of an