The nutrients in topsoil that support plant growth come from

The nutrients in topsoil that support plant growth come from plant and animal matter that is decaying.
When a plant or an animal is decaying, it releases nutrients which are beneficial for the soil. If the soil is healthy and thriving, it means that the new plants which are about to appear will grow more healthily and produce their 'goods.'

Most of the land is used for housing/commercial uses

Conflicts arising from drug cartels and goverment corruption is an issue that would most likely be considered as mexico's most challenging problem of today. the correct option among all the options that are given in the question is the third option or option "c". this problem has continued for a very long time.