Question

I looked _____ the door fillin the blanks behind/out

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Answer 1

Answer:

i looked at the door it is tha answer

Answer 2

Answer:

I looked behind the door is the correct answer.

Explanation:

'Look out' is a phrase used for being careful. For example, Look out for the dogs in the society.

Whereas 'Look behind'  is normally used for looking at something which is behind or at your back side. For example, Look behind your car.

So, look behind is the correct word to be used in the given sentence.