  Recently discovered bursts of gravitational waves provide a good opportunity
to verify the current view on the evolution of close binary stars. Modern
population synthesis computer programs help to study this evolution from two
main sequence stars up to the formation of compact remnants. To calculate the
evolution of predecessors of black hole (BH) mergers we used the `Scenario
Machine' code. The scenario modelling allowed to describe the evolution of
systems for which the final stage is a BH+BH merger and showed the plausibility
of modern evolutionary scenarios for binary stars and population synthesis
models based on it. We discuss possible values of spins in BH mergers, and give
arguments in favour of different values of spins of BH components in BH mergers
(low spin + low spin, low spin + high spin, high spin + high spin). We predict
that $\geq 50\%$ BH mergers originated through isolated binary evolution should
possess spins of both BHs close to zero (low spin + low spin). Up to
$\approx$10\% of BH mergers are able to consist of two BHs with spins close to
one (high spin + high spin), predecessors of such binaries could be sources of
two gamma ray bursts. The BH with the spin close to one could be formed as the
result of the merger of two BHs formed via the collapse of a fast rotating star
accompanied with a long gamma ray burst and/or a gravitational wave burst with
smaller power in comparison with the merger of two BH remnants of binary
components.
