How might bird species A and B come into contact with DDT, a pesticide used by farmers?

By birds that ate or were in contact with plants that were sprayed with DDT .

Explanation:

(DDT) is a versatile pesticide used in agriculture to combat insect plagues. DDT has been prohibited  in many contries because this insecticide might cause health problems in humans, especially during fetal development.

•there must be variation for the particular trait within a population.

•the variation must be inheritable (that is, it must be capable of being passed on from the parents to their offspring).

•individuals with one version of the trait must produce more offspring than those with a different version of the trait.good

explanation:

a covalent bond, specfically triple bond