None of those listed. This is a bad question.
Your teacher probably wants
A. The traits are governed by genes on different chromosomes.
Why that's bad:
You can look up a list of Mendelian traits and find that some of them are on the same chromosomes. Independent assortment can occur as long as the tested gene loci are on the opposite ends of the chromosome: crossover can occur often enough between them.
Even so, there are a couple of pairs that are close enough so that Mendel should have discovered linkage.
I suspect that he DID discover linkage, but that either he, or his assistants, threw out the data because it didn't match the 9:3:3:1 expectations.
You can google for
if you like.
B: nope, that results in linkage (depending on how close the loci are), and not the 9:3:3:1 ratio.
C: The making of Mendel's true-breeding strains would have eliminated anything other than the two alleles per gene locus of interest. It's not an assumption, it's something that Mendel and his assistants made sure of.
D. That's a negatory. See C above.