A student research group at a school conducted an experiment to study the relationship between the germination rate $y$ of a certain crop seed and temperature $x$ (in units of ${}^{\circ}\mathrm{C}$). Under 20 different temperature conditions, seed germination experiments were performed. From the experimental data $\left( x _ { i } , y _ { i } \right)$ ($i = 1,2 , \cdots , 20$), a scatter plot was obtained. From this scatter plot, between $10^{\circ}\mathrm{C}$ and $40^{\circ}\mathrm{C}$, which of the following four regression equation types is most suitable as the regression equation type for the germination rate $y$ and temperature $x$? A. $y = a + b x$ B. $y = a + b x ^ { 2 }$ C. $y = a + b e ^ { x }$ D. $y = a + b \ln x$
A student research group at a school conducted an experiment to study the relationship between the germination rate $y$ of a certain crop seed and temperature $x$ (in units of ${}^{\circ}\mathrm{C}$). Under 20 different temperature conditions, seed germination experiments were performed. From the experimental data $\left( x _ { i } , y _ { i } \right)$ ($i = 1,2 , \cdots , 20$), a scatter plot was obtained. From this scatter plot, between $10^{\circ}\mathrm{C}$ and $40^{\circ}\mathrm{C}$, which of the following four regression equation types is most suitable as the regression equation type for the germination rate $y$ and temperature $x$?\\
A. $y = a + b x$\\
B. $y = a + b x ^ { 2 }$\\
C. $y = a + b e ^ { x }$\\
D. $y = a + b \ln x$