Spearman Inferred the Existence of a G Factor in Intelligence

Multiple Choice

Spearman inferred the existence of a g factor in intelligence from what evidence?​

A) Mean performance on IQ tests has been rising from one generation to the next.
B) ​Scores on any intellectual test correlate positively with almost any other such test.
C) ​Scores on IQ tests are consistently higher in prosperous countries than in poor countries.
D) ​Children's scores on IQ tests correlate highly with those of their parents.