The word effective” in paragraph 2 is closest in meaning to .

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 29 to 33.
For wild animals, there is only one rule for survival: eat or be eaten. To survive in this difficult world, many animals have developed interesting techniques. Some animals make loud noises to scare off their enemies. Others give off a strange and unpleasant smell. The most common way for animals to avoid being seen is to use camouflage to blend in with their environment.
Blending in with the environment allows animals to either hide from animals that would want to eat them or sneak up on animals they would like to eat without being seen. Male birds are brightly coloured in order to attract mates, but female and baby birds usually have dull brown or grey colours. This makes them difficult for their enemies to see. When they stay very still, they blend in with the tree branches around them. It's a very effective protection method.
Interestingly, tigers use their colouration for a different reason. The tiger's orange and black stripes blend in with the grass and shadows of the jungle. This allows them to creep close enough to their prey without being seen. Once the tiger is within striking range, it can leap from the shadows and attack before its prey has time to escape.
Whether it's blending with the environment to eat or to avoid being eaten, camouflage is a great adaptation. The next time you see an animal with interesting colours, ask yourself why the animal is coloured the way it is. It may serve more than making the animal look beautiful.