$\text{I. B.}$

${\text{a}}^5\cdot {\text{a}}^7\cdot {\text{a}}^9\cdot {\text{a}}^8={\text{a}}^{5+7+9+8}={\text{a}}^{29}$ ${\text{a}}^5\cdot {\text{a}}^7\cdot {\text{a}}^9\cdot {\text{a}}^8={\text{a}}^{5+7+9+8}={\text{a}}^{29}$

 

$\text{II. B}$

${\text{x}}^4\cdot {\text{x}}^1\cdot {\text{x}}^1\cdot {\text{x}}^{15}={\text{x}}^{4+7+1+15}={\text{x}}^{27}$

 

$\text{III. A}$

${\text{y}}^8\cdot {\text{y}}^{15}\cdot \text{y}\cdot {\text{y}}^0\cdot {\text{y}}^{17}={\text{y}}^{8+15+1+0+17}={\text{y}}^{41}$