Which of the following is the best example of evolution occurring?

a. lions and cows both have hair covering their bodies and give birth to live offspring.
b. some of the trees in places with harsh winters lose their leaves in the fall.
c. strains of bacteria can become immune to antibiotics that once killed them effectively.
d. viruses can attack single-celled organisms as well as multicellular organisms.

The correct answer is - C. Strains of bacteria can become immune to antibiotics that once killed them effectively.

One of the best examples where we can witness the evolution taking place are the bacteria. The bacteria can be very dangerous, so because of that people created antibiotics in order to control it or destroy it. But the bacteria has shown on multiple occasions that it actually is able to develop immunity to the antibiotics after few generations. Because of that, new antibiotics are constantly made in order to cope with the bacteria, but it constantly manages to strengthen its immune system, so its an ever going battle between the evolution of the bacteria and the scientists that try to kill it.

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

: -)