问题如下：
1.Based on Exhibits 1 and 2, if Liu were to graph the 50 observations, the scatterplot summarizing this relation would be best described as:
选项：
A.horizontal.
B.upward sloping.
C.downward sloping.
解释：
C is correct
because the slope coefficient (Exhibit 2) and the cross-product (Exhibit 1) are negative.
看了答案，想问下，只用slope coefficient为负判断是向下倾斜可以吗？
