Question

When I entered into the room I saw my friends __________ (watch) a movie.
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Answer 1

when I entered into the room I saw my friends WATCHING a movie

Answer 2

The complete sentence will be:

When I entered the room, I saw my friends watching a movie.

[ 'entered into' is a wrong expression as entered itself refers to going inside and hence the usage of 'into' becomes redundant in this case]

* The given sentence is in the past tense where an event in the past has been stated.

* The continuous form of the verb has been used here, i.e. watching for watch. It is because the action was in motion at that point of time.

* Continuous tense can be in the present, past or future form depending on its usage.