The principle the trainer adopted is Specific adaptation imposed demand.
It describe specific adaptation imposed demand because In SAID principle, different sports posses its own unique demand and in order to improve skills base on a particular sports, human body adapts to the imposed demands by practicing the sports unique moves to asserts the sport demand.
I think the correct answer from the choices listed above is the last option. The control group to be used to test the hypothesis would be the swallows with average-length tails. A control group <span>is defined as the </span>group<span> in an experiment or study that does not receive treatment by the researchers.</span>