$1.$ A bioengineering textbook reports the Young$$s modulus and shear modulus of cortical bone to be $18$ GPa and $6$ GPa, respectively. What do these material constants represent, and how are they different from one another?

$2.$The figure below shows stress$-$strain curves for both wet and dry human femoral bones loaded to failure. Which material is more brittle? How can you tell? $($Note that the units of stress are given as $103$ lb$/$in$2.)$