A pink unicorn is crossed with a blue unicorn and all of the offspring are lilac, caused by the presence of both pink and blue hair. This is an example of alleles that are .

The correct answer is codominant.

Explanation:

A phenomenon in which two heterozygous alleles get expressed completely in the offspring produced is termed as codominance, and the trait produced is termed as a codominant trait. In codominance, both the alleles show their presence, that is, none of them is considered dominant, and like incomplete dominance, the alleles do not get mixed up.  

For example, in the given case, the crossing between a pink unicorn and a blue unicorn produces an offspring, which is demonstrating both pink and blue color fur. This shows that the phenomenon of codominance is taking place and the produced trait is an illustration of codominant trait, as the produced offspring is having both pink and blue color hair.  

the correct answer is:

a population changes in response to a change in the environment.