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"He walked slowly because of his bad leg."
In the above sentence "because of" acts as a preposition.
But when we write it as "It was because of his bad leg that he walked slowly", "it" refers to the nominal clause "that he walked slowly".
So the sentence can be written as "That he walked slowly was because of his bad leg"
So the sentence takes the form , Noun + be + because of + Noun.
Shouldn't there be another verb in the sentence after the linking verb "be" to make the above sentence as well the original sentence "It was because of his bad leg that he walked slowly" grammatically correct ?
Comments  
Hi,
because of is a phrasal preposition, but not just preposition.
Regards,
sri
But it is still a preposition.
We don't write "The accident was because of me"
We write "The accident took place because of me."
We don't just use a linking verb.