In general, the more complex the model, the greater the chance of:
a. Overfitting the data.
b. Underfitting the data.
c. Pruning the data.
d. The need to reduce the amount of data considered.

A). Overfitting the data.

Explanation:

As per the question, the more complex a statistical model is, the greater the chances of 'overfitting of the data' because the complexity would lead the model to suffer failure of coping up with the additional data that would influence the predictive ability of the model. Such a failure or overfitting of data occurs when the model contains the excessive number of data points that could be explained by data which eventually brings the failure of the model as the function is too closely being laid out. Therefore, option A is the correct answer.

answer; i believe the correct answer is (a) the correlation between the cause variable and outcome variable is zero;

well considering i can't see the graph, it's probably prices