Danny wants to improve his technique for punting the football, so he devises an experiment to . he goes to the field with 5 different kinds of shoes, thinking that with his experience level, the type of shoe might make a difference. he kicks the ball 10 times with each shoe and measures the distance it went. he uses 3 types of shoes on monday, but because it got dark earlier than expected, has to complete the test on tuesday. what is a major change danny should make, to increase the validity of his test? a) do all his tests on one day b) measure how tight the shoes were c) measure the pressure in the football d) do his tests on different parts of the field