Which is the correct way to punctuate the sentence?
(A) Dr. Burke wanted to trust her assistant with the secret formula; but she was afraid her assistant was a spy.
(B) Dr. Burke wanted to trust her assistant, with the secret formula: but she was afraid her assistant was a spy.
(C) Dr. Burke wanted to trust her assistant with the secret formula but, she was afraid her assistant was a spy.
(D) Dr. Burke wanted to trust her assistant with the secret formula, but she was afraid her assistant was a spy. ​

Which is the correct way to punctuate the sentence A Dr Burke wanted to trust her assistant with the secret formula but she was afraid her assistant was a spy B class=