B There are no professional restrictions for applying for the exam. University students can directly take the cross-level exam, that is, senior nutritionists, and they can directly take the second-level exam (technician level) 3-5 years after graduation.
C textbook is designated by the state, and there are two books in Level 3, one of which is called "Public Nutritionist" (Level 3). The other is "basic knowledge", including selection, analysis, short answer and practical operation (measuring height and weight). Not difficult. Many of my friends have taught themselves.
D Because the provincial offices don't accept individual registration, if students are not organized by the school or have graduated, they should look for local training or newspapers. I suggest you consult more, dear friend. Registration is very cheap, training 1500-2500 ~ ~