Use of antibiotics in animal feed leads to antibiotic-resistant bacteria because

The correct option is D.

Explanation: The options attached to this question are given below:

A) Bacteria from other animals replace those killed by the antibiotics.

B) The few surviving bacteria that are affected by the antibiotics develop immunity to the antibiotics, which they pass on to their progeny.

C) The antibiotics cause new mutations to occur in the surviving bacteria, which results in resistance to antibiotics.  

D) The antibiotics kill susceptible bacteria, but the few that are naturally resistant live and reproduce, and their progeny repopulate the host animal.

E) The antibiotics persist in soil and water.

Antibiotics are sometimes used in animals to control infections. With time, the microbes that are been targeted with the antibiotics usually develop mutations, which makes the antibiotics to become ineffective, thus, the antibiotics will only be able to kill the susceptible microbes while the ones that have developed resistance will remain and give birth to young ones that are also resistant to antibiotics.