First, he should measure how long it takes for the liquid to become clear if X and Y are mixed together. Then, he should measure how long it takes if he also adds substance A to X and Y. He will find out if substance A is a catalyst. hope this helps :)
Water gains energy during evaporation and releases it during condensation.
Simple organic molecules can be organized into much longer, more complex molecules.
1: over population
2:disease
3: Darwinism.
