In a dihybrid cross, the 9:3:3:1 ratio is obtained?

A is wrong.  If the two genes are linked the alleles will be inherited together and you will get a 3:1 ratio of parental traits.

B is correct. There is a nice diagram of how it happens here http://en.wikipedia.org/wiki/File:Dihybrid_cross.png

C is sometimes correct.  If the two genes are far enough apart from each other, you will get 50% crossing over which gives the same offspring ratio as if the two genes are on separate chromosomes.   This was actually the case with several of the traits that Mendel looked at in his original experiments.

Since A is wrong, D is wrong.  Since B is always right, E is wrong.