Answer:
D. inferred causation from correlation
Step-by-step explanation:
Causation is the condition that a change in one variable is the result of the other variable changing i.e., one variable causes the change in the other variable.
Correlation is the condition where the change in one variable causes the change in the variable but they may directly not influence each other. One variable may cause change in a different variable which causes a change in the other variable.
Here, it has been inferred that the reason for the children's better grades is the presence of an encyclopedia. However, a direct link between these two variables has not been established.
Hence, the answer is D. inferred causation from correlation.