123. The total weight will increase $20\times 20\times 20=8000$ times, but the bone strength will only increase $20\times 20=400$ times, so its bones would break under its weight.

125. No because the domain of any polynomial function is $(-\infty ,\infty ),$ which includes the point $x=0$

127. Not possible; this is inconsistent with its end behavior.

129. $P\circ Q$ is a polynomial of degree $m\cdot n$.