Which of the following is the most accurate description of multicollinearity in multiple regression?

a. It implies that if each explanatory variable were regressed against the other explanatory variables, the resulting R-square values would all be quite large.

b. It implies that at least one pair of explanatory variables are highly positively correlated.

c. It implies that all correlations between pairs of explanatory variables are quite large in magnitude.

d. It implies that at least one correlation between a pair of explanatory variables is quite large in magnitude.