The author refers to the somewhat lower urinary kallikrein levels in black children in order to ______.
A．support the thesis that kallikrein levels are inversely related to blood pressure
B．highlight the special health problems involved in treating populations with high concentrations of black children
C．offer a causal explanation for the difference in urinary kallikrein levels between black and white children
D．suggest that further study needs to be done on the problem of high blood pressure among black adults