  Solution of the Schr\"odinger's equation in the zero order WKB approximation
is analyzed. We observe and investigate several remarkable features of the
WKB$_0$ method. Solution in the whole region is built with the help of simple
connection formulas we derive from basic requirements of continuity and
finiteness for the wave function in quantum mechanics. We show that, for
conservative quantum systems, not only total energy, but also momentum is the
constant of motion. We derive the quantization conditions for two and more
turning point problems. Exact energy eigenvalues for solvable and some
``insoluble'' potentials are obtained. The eigenfunctions have the form of a
standing wave, $A_n\cos(k_nx+\delta_n)$, and are the asymptote of the exact
solution.
