A pure substance is any substance on its own. For example, sand is impure for containing lots of different substances. However, diamonds are mostly pure for only containing one type of substance.
Whether a substance is pure or not doesn't relate to a substance's molecular structure, but different molecules in a substance. Water by itself is only H2O, therefore it still pure.
Water is not an element but a compound for containing different elements, however it still pure.
b. digestion and photosynthesis.
c. photosynthesis and respiration.
d. aerobic and anaerobic respiration.
Answer: C. photosynthesis and respiration.
Explanation:
mountains
depressions
discontinuities
The answer is depressions. I just completed the quiz.