and H[ii]{} regions {#sect:select}
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Procedure of identification and preliminary selection of star formation regions on $B$ and H$\alpha$ images of galaxies using the [SExtractor]{}[^3] program was described in detail in @gusev2018.

Coordinates of all objects (star clusters on $B$ images and H[ii]{} regions on H$\alpha$ images) were recalculated for the deprojected positions using position angles and inclinations of the galaxies by standard formulae. In the next step, we determined the separation, $S$, between a star cluster and the nearest H[ii]{} region (SC-H[ii]{}R pair) for all selected star clusters. Herewith, we suggest that a single H[ii]{} region may be paired with up to multiple star clusters.

The relation between colour indices of young star clusters and their separations is given in Fig. \[figure:ubv\_sep\]. Unlike Fig. 3 in @gusev2018, Fig. \[figure:ubv\_sep\] shows deprojected angular separations.

@whitmore2011 showed that the morphology of ionized gas bubbles can be used as an age indicator of star clusters. Unfortunately, we are not able to study the H[ii]{} morphology directly on scales of $<40$ pc, because our angular resolution is 1-1.5 arcsec. However, as was shown in @gusev2016, the distance between photometric centres of gas emission and star clusters correlates within a single star formation region 