Our understanding of the role played by genes in many human characteristics is advancing rapidly in, for example, body size, performance on IQ tests, and personality traits. In this new genetic era, the role of the environment __________.

a. is to work with genes in complex and often unknown ways in the development of these traits

b. is always far more important than genes in the development of complex human traits

c. is important only in influencing personality traits can largely be discounted in the development of complex human traits