Tail-Feather Length in Birds Is Sometimes a Sexually Dimorphic Trait

Multiple Choice

Tail-feather length in birds is sometimes a sexually dimorphic trait. That is, the trait differs substantially for males and for females. Researchers studied the relationship between tail-feather length (measuring the R1 central tail feather) and weight in a sample of 20 male and 21 female long-tailed finches raised in an aviary.
What is a practical interpretation of the slope estimate of the least squares regression line for males (blue squares) ?

A) For each additional gram of weight, we estimate the tail feather length to increase by 3 mm, on average.
B) For each additional gram of weight, we estimate the tail feather length to increase by 70 mm, on average.
C) For each additional millimeter of length of tail feather, we estimate weight to increase by 3 g, on average.
D) For each additional millimeter of length of tail feather, we estimate weight to increase by 70 g, on average.