Which topsoil is the most fertile? 

A)  yellow 
B)  red 
C)  grey 
D)  dark brown or black

Dark brown or black topsoil is typically the most fertile because it contains high levels of organic matter, nutrients, and microorganisms that support plant growth. Yellow, red, and grey topsoils can also be fertile, but their fertility levels depend on various factors such as climate, vegetation, and soil management practices.