Use the Product Rule to Simplify the Expression $2 ^ { 5 } \cdot 2 ^ { 4 }$

Multiple Choice

Use the product rule to simplify the expression. Write the result using exponents.
- $2 ^ { 5 } \cdot 2 ^ { 4 }$

A) $2 ^ { 9 }$
B) $2 ^ {20 }$
C) $4^ { 20 }$
D) $4 ^ { 9 }$