When I mosaic L2A images,the resolution is changed

Hello every,please help me
I downloaded 7 L2A images,now I want to mosaic them .But when I finish mosaicing ,the resolution is changed and now it’s resolution is 1 km .
Before I mosaic them ,I select 4 bands (red, blue, green,and NIR, all resolution are 10 m)

I use the tool (Raster>Geometric operations>Mosaicing)
I also tried this tool (Raster>Geometric operation>Multi-size mosaic )with my raw Sentinel-2 L2A products before, but the result is a pure gray image without any data.

If you use the generic mosaic tool you need to specify the desired resolution in degree.

For the issue with the multi-size mosaic maybe @kraftek or @obarrilero can help

Many thanks for your reply.:grinning: