(A) there are general surgeons who are incompetent The argument says that surgery at the hands of anyone other than a general surgeon involves highly undesirable risks. The argument does not say that surgery at the hands of general surgeon does not pose risks. We cannot just assume that.
(B) general surgeons are not the only doctors competent to perform surgery This seems to be the right answer. If other doctors are competent, then surgery at the hands of other doctors except general surgeon seems possible.
(C) the competence of the doctor performing surgery does not guarantee a successful outcome But how does it matter? Again, the argument says that surgery at the hands of anyone other than a general surgeon involves highly undesirable risks. The argument does not say that surgery at the hands of general surgeon does not pose risks. We cannot just assume that.
(D) risk is not the only factor in deciding whether to have surgery There might be other factors involved or there might not be. Why do we care?
(E) factors in addition to competence are relevant when choosing a doctor Again, there might be other factors involved or there might not be. Why do we care?
Hence, the answer must be (B)