Answer:
Your answer would be A.
Step-by-step explanation:
Sentence A uses the absollute phrase arms folded across his chest to add variety and interest to its meaning. An absolute phrase is a phrase that modifies a noun in a sentence, but it is not connected to the sentence by a conjunction. It is offset with a comma and can be removed withouth chaning the meaning of the sentence.
In this case, the absollute phrase above modifies the noun Dr. Ley. As it has been said, this absolute phrase can be removed without changing the meaning of the sentence (see II).
I) Arms folded across his chest, Dr. Ley lectured the class sternly about the evils of plagiarism.
II) Dr. Ley lectured the class sternely about the evils of plagiarism