The photosynthesis is a process in which the plants capture the sunlight in order to obtain energy. One of the results is that oxygen is released as well. To achieve that, the plant take in carbon dioxide (CO2) from the air, which can be released during animal respiration, and water (H2O) from the soil, releasing oxygen in the end of the process. In this flowchart, the plants should be eaten by animals after the oxygen is released (so, letter A is incorrect), and the plants take in water from the soil, not the opposite (which means that letter B is also incorrect). Also, the animals must breathe out carbon dioxide before the process, because CO2 must be already available. So, the plant must use CO2 and H2O (carbon dioxide and water) to obtain sugar and release oxygen. Therefore, the correct answer is d) Carbon dioxide and water are used to make sugar.