With blood pressure held at a constant value, which of the following combinations will raise the glomerular filtration rate above the baseline value?
a) Constriction of the afferent arteriole and dilation of the efferent arteriole
b) Dilation of the afferent arteriole and constriction of the efferent arteriole
c) Constriction of both the afferent and efferent arterioles
d) Dilation of both the afferent and efferent arterioles