How does crossing over mix up alleles from your paternal and maternal chromosomes:
a. it causes alleles on the same chromosome to be inherited together
b. it involves a physical exchange of segments from homologous chramosomes.
c. it allows male and female gametes to combine randomly at fertilization.
d. it causes alleles on nonhomologous chromosomes to be inherited independently.

b. it involves a physical exchange of segments from homologous chramosomes.  

Explanation:

Crossing is a phenomenon involving homologous chromatids. It consists of the breaking of these chromatids at certain points, followed by an exchange of corresponding pieces between them.

Exchanges cause new gene sequences to appear along the chromosomes. Thus, if on a chromosome there are several genes combined in a certain sequence, after the occurrence of crossing the combination may no longer be the same. So when thinking about crossing, it is common to analyze what would happen, for example, about the combination of the allele genes "A" and "a" and "B" and "b" in the pair of homologues.

it's anything that aren't producers and consumers.

explanation:

you've got to be clear on what "this" is

c

explanation: