The sales of air conditioners and sales of electric fans in a local appliance store are recorded daily during July 1 to July 31. A least squares regression line that predicts daily sales of air conditioners (y) from daily sales of electric fans (x) is fitted to the data, and found to be have a slope of 0.98. Which of the following statements must be true?

A. The correlation between the daily sales of air conditioners and the daily sales of electric fans in July is very strong because the slope is close to 1.
B. It is reliable to use the fitted regression line to predict daily sales of air conditioners from daily sales of electric fans for the month of August.
C. The residual plot shows a positive trend.
D. An increase in the daily sales of electric fans causes an increase in the daily sales of air conditioners in July.
E. None of the above.