Why are new copper extraction methods needed?

The correct option is High-grade copper ores are becoming scarce. This answer is correct because it matches the approved learning objective to explain how harvested plants are burned to produce ash containing metal compounds. (HT only) in the subtopic Alternative methods of extracting metals.

The correct option is High-grade copper ores are becoming scarce. High-grade copper ores are becoming scarce is correct because it directly supports the approved learning objective to explain how harvested plants are burned to produce ash containing metal compounds. (HT only). This belongs to the subtopic Alternative methods of extracting metals within Using the Earth's resources and obtaining potable water, so the explanation must stay tied to that curriculum context. The other options are incorrect because they either do not answer this learning objective, use a vague statement, or move away from Alternative methods of extracting metals.