The length of a parallel of λ latitude between two meridians is equal to difference in longitudes multiplied by

Answer: Option B

In surveying, the length of a parallel of latitude (λ) between two meridians is equal to the difference in longitudes multiplied by the cosine of the latitude (λ). This relationship arises from the spherical geometry of the Earth's surface. As you move away from the equator towards the poles, the parallels of latitude become shorter due to the convergence of meridians towards the poles. The cosine of the latitude accounts for this reduction in length as you move away from the equator. Therefore, the correct option is Option B: cos λ.