When blood glucose levels rise…such regulation of blood glucose levels is an example of?

When blood glucose levels rise, the pancreas secretes insulin and as a result blood glucose levels decline. When blood glucose levels are low, the pancreas secretes glucagons and as a result the blood glucose levels rise. Such regulation of blood glucose levels is an example of
a) feedforward mechanism
b) positive feedback
c) negative feedback
d) feedback inhibition
e) both c and d

It should be C.

It falls under the principles of homeostasis:
stimulus (receptor), set point, effector, negative feedback. The control center determines an appropriate response to the stimulus. The result of that response feeds to the effector, either enhancing it with positive feedback or depressing it with negative feedback.

Hence the regulation of blood glucose level is via negative feedback because the feedback produces an opposite effect to the change.

EDIT: went to search for a source as well (read under Control Mechanisms)

Davos Annual Meeting 2010 – Rethinking Trade and Climate Change