Most nations have exhibited substantial increases in iq scores during the past century. this phenomenon is called the

The answer to this question is called a Flynn Effect.

 A Flynn Effect is a situation where in the intelligence test scores increases over a period of time. The Flynn Effect was named after an intelligence researcher named James Robert Flynn. In Flynn’s discovery, he found out that IQ scores increases because the level of education is also increasing adding knowledge to students.

it should be d or b but i'm sure it's d

answer; through play and social interaction;