Test cross biology

answer is A
i cant seem to understand this style of showing crosses. can someone explain?


test cross is crossing a homozygous recessive individual with an individual of known phenotype but unknown genotype
that leaves option A) and C)
the offspring have ttBb and Ttbb genotype, which means the gametes underwent recombination TB//tb became Tb//tB after recombination
making Tb and tB gametes, after fetilization it gives Tb//tb and tB//tb offspring
answer must be A)

how do we read this type of double lined crosses? like what is the value in the upper and lower? that confuses me a lot

i don’t know, i read each line as if it were a chromatid, so on this chromosome the chromatids had the alleles tB and tb