Consider p(x)=xlnx on (0,∞). Which description best characterizes the concavity of p on the interval (1,e)?
a) p is concave up on the entire interval.
b) p changes concavity exactly once on the interval.
c) p is concave down on the entire interval.
d) p is concave down on (1,e) and concave up on (e,e).