Let's represent "x" as the number of students who choose band.
According to the proportion, the number of students in choir is four times the number of students in band. Therefore, the number of students in choir is 4x.
We know that the total number of students is 250, so we can set up the equation:
x + 4x = 250
Combining like terms:
5x = 250
Dividing both sides by 5:
x = 50
Therefore, the answer is C. 50 students can choose band.