In trying to solve the pendulum problem, formal operational adolescents usually ________. Question 10 options: a) identify relevant variables and test each one separately and, if necessary, also in combination b) test changes in string length and changes in weight together before testing them in isolation c) are able to determine the effect of changing the force of the initial push, but not other changes d) focus on only the weight of the object on the pendulum, and not the length of the string