Which of the following is typically NOT a method scientists use to determine astronomic distances?

Question

a. brightness as compared to other objects
b. color of the object
c. radio wave signature
d. the size an object in space appears

I think it's c but I could be wrong

Answer 1

I mean d

Answer 2

I think its b. How can color have anything to do with astronomical distances???

Answer 3

I was right, it is d.
(by color, I think they mean the color of the light, so yes that's a way)