The correct option is
B P R S T Q U
The first sentence in the sequence should be the one that introduces a new topic. It cannot be a phrase that is an extension or continuation of a topic.P is the first in sequence: P starts the discussion about how literacy magazines have been good because of their editors.
P is followed by R: R further bolsters P's point by telling how the behaviour of the editors affects the magazines. Q and S cannot follow P as they jump to unrelated topics, while R continues the topic. Thus, options A, C and D are incorrect.
R is followed by S: R finishes talking about the nature of editors and then S takes the discussion to number of editors. 'But' indicates a slight change in topic.
S is followed by T: T directly follows S by giving an example about the point made by S.
T is followed by Q: Q adds another point to the discussion. The word 'Furthermore' indicates that it is an additional point and not the main. Thus, it follows the point made by S and T.
Q is followed by U: After all the points are added, U provides a concluding statement. As it provides a conclusion, it is last.
Thus, the correct sequence is P R S T Q U. Hence, B is the correct option.