To solve this question, the user needs to know the definitions of the given options and the context of the sentence. The sentence describes a professor who is expressing his opinions forcefully, causing students to leave his course.

Now, let's go through each option and explain why it is right or wrong:

A. dormant: This option is incorrect. The word "dormant" means inactive or asleep, and it does not fit the context of the sentence. The professor is not inactive or asleep but rather expressing his opinions forcefully.

B. credible: This option is incorrect. The word "credible" means believable or trustworthy, and it does not fit the context of the sentence. The professor's opinions may or may not be credible, but the sentence is discussing the forceful expression of opinions.

C. dogmatic: This option is correct. The word "dogmatic" means expressing opinions in an arrogant or stubborn manner, which fits the context of the sentence. The professor is so forceful in expressing his opinions that it causes students to leave his course.

D. lucid: This option is incorrect. The word "lucid" means clear or easy to understand, and it does not fit the context of the sentence. The professor may or may not be expressing his opinions in a clear manner, but the sentence is focused on the forceful expression of opinions rather than clarity.

Therefore, the answer is: C. dogmatic.