Here we have a Strengthen with Necessary Premise question. Remember that a premise is necessary for a conclusion if the falsity of the premise guarantees or brings about the falsity of the conclusion. First, we check to see if the answer choice strengthens the passage, and then, if it does strengthen, we negate the answer choice to see if its negation makes the argument fall apart. If the answer choice does both those things, then it is our correct answer.
Our conclusion is: "The dean of computing must be a professor from this university's computer science department." Why? We know the person chosen for the dean of computing has to be respected by the academic staff and be competent to oversee the use of computers on campus. We know that the only deans whom academics respect are those who hold doctoral degrees, and only someone who really knows about computers can competently oversee the use of computers on campus. We also know that the board of trustees has decided that the dean of computing must be selected from among the university's staff.
Answer choice (B) states, "All of this university's professors have obtained doctoral degrees." Does this answer choice strengthen the passage? No. We know that the academic staff must respect the dean of computing and that the only deans whom academics respect are those who hold doctoral degrees. So, if a dean is respected, then that means that they hold a doctoral degree. Answer choice (B) tells us that all of this university's professors have obtained doctoral degrees. However, having a doctoral degree is not sufficient to be respected by academics, it is the necessary condition of being respected by academics. Merely knowing that all the professors in this university have obtained doctoral degrees does not support the argument that the dean of computing must be a professor from this university's computer science department.
Now, let's look at answer choice (E): "Among this university's staff members with doctoral degrees, only those in the computer science department really know about computers." Does this answer choice strengthen the passage? Yes. We know that the dean of computing must be respected by the academic staff and be competent to oversee the use of computers on campus. Further, we know that the board of trustees has decided that the dean of computing must be selected from among this university's staff. Answer choice (E) tells us that if one really knows about computers, then he or she is in the computer science department.
So, we know that to be able to completely oversee the computer science department, you must really know about computers, and if you really know about computers then you are from the computer science department of the university. So, in order to fulfill the requirement that the dean of computing must be competent to oversee the use of computers, he or she must be from the university's computer science department.
Now, does the negation of answer choice (E) make the answer fall apart? Yes. The negation of E is: "Among this university's staff members with doctoral degrees, not only those in the computer science department really know about computers."
Thus, it does not have to be true that the dean of computing MUST BE a professor from this university's computer science department because someone else could really know about computers, as well. Therefore, the negation of answer choice (E) makes the argument fall apart.
Hope that was helpful! Please let us know if you have any other questions.
