The majority of human traits are polygenic, which means they are
a.
determined by a single gene
b.
developed at birth
c.
influenced by multiple genes
d.
learned over time

The correct answer for the blank is-  

C.  influenced by multiple genes.

Polygenic traits are those characteristics of the individual that are controlled by more than one gene.

These traits depict wide range of variation in them.

For instance, human traits such as height, color of skin, color of eye are polygenic traits because they are influenced by multiple genes.

Thus, option C) is the right answer.