Refer to This Text to Answer the Following Questions

Multiple Choice

Refer to this text to answer the following questions.
To map genes of a bacterial strain,conjugation must be interrupted at given times.Suppose you have Hfr cells of genotype a⁺ᵇ⁺ᶜ⁺ᵈ⁺ᵉ⁺ˢᵗʳᴿ and F⁼ cells of genotype a⁻ᵇ⁻ᶜ⁻ᵈ⁻ᵉ⁻ˢᵗʳˢ and you combine these two cultures in liquid medium in four blenders at time 0.After intervals of 3,6,9,and 12 minutes,you turn on successive blenders.
-The resulting cultures were then plated on medium containing streptomycin.Why?

A) to eliminate non-conjugating Hfr cells
B) to eliminate all non-conjugated cells
C) to eliminate non-conjugated F⁻ cells
D) to selectively eliminate cells that have taken in F⁺ genes