Give reasons for the following:
$(a)$ Traits acquired during the lifetime of an individual are not inherited.
$(b)$ All human beings belong to a single species.
$(c)$ Variations keep on accumulating during reproduction and do not disappear in the next generation.

(N/A) Acquired traits do not cause any change in the $DNA$ of the germ cells of an organism,hence they are not inherited.
$(b)$ All humans,despite their diverse appearances,belong to a single species,$Homo$ $sapiens$. They originated in Africa and migrated across the globe. Differences in skin colour and physical features are merely adaptations to different environmental conditions and do not constitute speciation.
$(c)$ Inheritance from the previous generation provides a common basic body design along with subtle changes. These variations are passed on to the next generation,where they accumulate over successive generations.