It was observed that blood glucose levels were falling in an individual. this event would be sensed by (a) cells in the (b) of the pancreas, causing them to release the hormone (c). this series of events would be part of an (d) loop/mechanism, serving as a self-adjusting mechanism for maintaining normal levels of blood glucose.
i thought it was alpha cells in the islet of the pancreas releasing glucagon, but what is the loop?

c. earths continental crust is thicker than its lithosphere.

because, the lithosphere is the outermost layer of the earth/ 100 km thick and is defined by its machanical properties.the lithosphere contains oceanic and continental crust that varies in age and thickness across locations and geologic time. the lithosphere is the coolest layer of the earth in terms of temperature. the term lithosphere should not be confused with the use of "geosphere" which is used to indicate all of earth systems, including the atmosphere, hydrosphere   and biosphere. the surface of the earth can be divided into the continental crust and the oceanic crust.   the continental crust is made mostly of granite while the oceanic crust is made of basalt. the average thickness of the continental crust is 25 miles and the average thickness of the oceanic crust is 5 miles.   three types of rock, igneous, sedimentary, and metamorphic, make up the surface of the earth. that's why 3 option is preferable.