take the following example:
At the universities of Oxford and Cambridge the… of teachers and students is vẻy high.
A.proportion B.number C. ratio D. percentage
I wonder if A or c is right.Can u help me distinguish?Thanks!
C. ratio is the right answer, I think: ratio of; proportion between.
To me proportion of X to Y is correct. The same refers to ‘ratio’. I would pick up ’ number’. Or ‘percentage’.
According to my dictionary, we have 2 structure:
1-Proportion of A and B(no structure proportion between)
2-Ratio of A and B
I couldn’t find ‘proportion between’, only ‘the proportion of something to something’ in the meaning of ‘the relationship between two things in size, amount, importance etc’
And I think (just intuition 
), ratio is the right answer.
The ratio of nursing staff to doctors is 2:1.
Well, I’d admit that ‘proportion between’ is not the key point to determine the right answer for the question but it’s possible, such as:
All the best.
I think more context is needed in order to give an opinion.
“number” seems to be a good choice.
just a student.
… may be
This is a very odd question.
“…the number of students and teachers” simply refers to how many there are. Perhaps it’s the right answer after all, but it’s not every natural.
I’m used to seeing “the ratio of X to Y” and there is only an “and” there, not a “to.”
I use proportion the same as ratio - the proportion of X to y.
Experience, however, tells you that it’s common to talk about the student:teacher ratio (or teacher:student ratio, if it’s in reverse). We don’t talk about the “proportion” of teachers in relation to students, but the ratio.