First of all, for the first two items, if A is correct, then B is also correct, so the first two items can be excluded. If point C is the midpoint, λ=0.5,

1/λ=2, what is μ? Without this μ, c is not the midpoint, and similarly, d is not the midpoint.

Looking at c again, if the CD is on the line segment AB at the same time, there are λ < 1, μ < 1, λ, μ > 0, then 1/λ+ 1/μ > 2, which does not meet the requirements of the topic and is discarded.

Finally, look at d, if CD is on the extension line of AB line at the same time, there is λ >; 1, or λ < 0, and the same is true for μ. In these cases, there is always 1/λ.

To sum up, choose D.