Weather forecast in Yinzhou District, Ningbo

A, understand the annual per capita income of residents in Yinzhou District, with a large number of people and heavy workload, which is suitable for sampling survey, so the choice is wrong;

B, given the weather forecast ratings of Yinzhou TV station, the census is of little significance and suitable for sampling survey, so the selection is wrong;

C, I learned that a middle school in Yinzhou District failed the math period, and the workload was small and lossless, so it was suitable for the general survey, so the choice was correct;

D, understand the population flow leaving Yinzhou District on a certain day, the number is large and the scope is wide, so it is appropriate to take spot checks, so the choice is wrong.

So choose: C.