5. The equation $x+2^{x}+\log 2 x=0$ has $(\quad)$ roots.
A. 0
B. 1
C. 2
D. 3
5. B

Let $f(x)=x+2^{x}+\log 2 x$, then $f(x)$ is a monotonically increasing function, because $f\left(2^{-10}\right)=2^{-10}+2^{2-10}+\log 2^{2-10}0$.

Therefore, there must exist and only exist one $x_{0}, 2^{-10}<x_{0}<1$ such that $f\left(x_{0}\right)=0$.