The correct answer is C. with.
The preposition “with” is used to indicate the means or instrument by which something is done. In this case, the lawyer was threatened with dire consequences. This means that the person threatening the lawyer was using dire consequences as a means to get the lawyer to do something.
The other options are incorrect because they do not indicate the means or instrument by which the lawyer was threatened. The preposition “from” indicates the source of something. In this case, the lawyer was not threatened from dire consequences. The preposition “by” indicates the agent or cause of something. In this case, the lawyer was not threatened by dire consequences. The preposition “of” indicates the possession or ownership of something. In this case, the lawyer was not threatened of dire consequences.