To simplify the expression \(100^3 \cdot 100^7\) using the Product Rule of Exponents, you would add the exponents together. The Product Rule states that when multiplying like bases, you can add their exponents:
\[ a^m \cdot a^n = a^{m+n} \]
In this case:
\[ 100^3 \cdot 100^7 = 100^{3+7} = 100^{10} \]
So, the correct simplification is \(100^{10}\).