We know that
African grey parrots cannot detect colors with wavelengths ≥ 620 nanometers.
We need to find out if African grey parrot detect color W
Given the statements
(1) Color V has a wavelength of 300 nanometers.
This tells us something about color V, but not about color W
So, Statement (1) alone is insufficient
(2) The wavelength of color W is twice that of color V.
Here we are told the wavelength of W in terms of V, but we are not given what V is
So, Statement (2) alone is insufficient.
Now lets combine statements (1) and (2)
Wavelength of V = 300 nm
Wavelength of W = 2 * V= 2*300 = 600 nm
Considering the fact that African grey parrots cannot detect colors with wavelengths ≥ 620 nanometers and W is of 600nm
We can say that the African grey parrot can detect the color W
C. Both statements together are sufficient, but neither alone is sufficient.