sexual mode of reproduction speeds up the process of making variants explain.

Variations are brought about by changes in the genome of an organism. During sexual reproduction a new organism is formed by the combination of genomes of two different individuals which will definitely give rise to variations from either of the two parental genomes involved. So it is the quickest and safest way of giving rise to variants. All other methods like mutations require time and certain forces, like they should be homozygous to be expressed, or should be selected to be carried forward. These features make all other methods slow and unsure way of giving rise to variants.