two pure substances, a and z, are to be identified. pure substance a can be broken down by a chemical change. pure substance z cannot be broken down by a chemical change. what can be concluded about these pure substances?

How should the syntax in this sentence be changed, if at all? the scientists spent years analyzing the results of numerous medical studies meant to identify the cause of the disease. no change the scientists spent years looking at the results of a variety of different medical studies meant to locate the cause of the disease. the scientists spent years reviewing medical study results to find the cause of the disease. the scientists spent years studying the results of many medical studies in order to uncover the cause of the disease.