Which of the Following Situations Is Best Addressed by Regression

Which of the following situations is best addressed by regression?

A) Is there an association between market share and size of the sales force after adjusting for the effect of sales promotion?
B) Are consumers' perceptions of quality related to their perceptions of prices when the effect of brand image is controlled?
C) Is there an association between market share and the size of the sales force?
D) Determine how much of the variation in the dependent variable (store sales) can be explained by the independent variables (price and level of advertisement) .