Which of the following statements is true about heritability?

a. Heritability allows a person to determine how much of his or her intelligence is determined by genetics.
b. A trait with high heritability generally cannot be modified by experience.
c. If a trait is determined to be highly heritable in one environment, it will be so in all environments.
d. Heritability cannot be directly measured; it must be inferred based on studies of people with a known degree of genetic similarity.