4. The smallest real value of $x$ that satisfies the inequality $9^{x}-2 \times 3^{x}-3 \geqslant 0$ is ( ).
(A) -1
(B) 0
(C) 1
(D) 3
4.C.

Let $3^{x}=t$. The original inequality can be transformed into $t^{2}-2 t-3 \geqslant 0$.
Solving this, we get $t \in(-\infty,-1] \cup[3,+\infty)$.
Since $t$ is positive, we have $3^{x}=t \geqslant 3$. Therefore, $x \geqslant 1$.
Thus, the smallest real value of $x$ that satisfies $9^{x}-2 \times 3^{x}-3 \geqslant 0$ is 1.