To simplify the expression \( x^3 \times x^4 \) using the product rule, we can use the property of exponents that states \( a^m \times a^n = a^{m+n} \).
In this case:
\[ x^3 \times x^4 = x^{3+4} = x^7 \]
So the correct choice is:
A. \( x^3 \times x^4 = x^7 \)