Main problems of weather system

A, C-D are controlled by low pressure, and it is rainy weather, which does not meet the meaning of the question;

B according to the barometric data, n is the low pressure center and m is the high pressure center. A and B are near the ridge of high pressure, and the weather is fine and correct under the control of the ridge of high pressure;

C, a is sunny and c is rainy, so it doesn't meet the meaning of the question;

D, B is sunny and D is rainy.

Therefore, choose: B.