Why are alleles on the same chromosome not always inherented jointly?

Alleles positioned on the same chromosome are not always inherited together because during meiosis linked genes can became separate genes.

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.

the backbone of the dna and rna compound is sugar phosphate.