Environmentalists are concerned about how our planet can sustain the growing human population with a limited - amount - of land and water.

• A. amount
• B. number
• C. quantity
• D. total

Answer: (A)

The main idea here is choosing the right quantifier for nouns that aren’t counted as individual items. Land and water are treated as a bulk resource rather than a list of countable units, so we use amount to express their measurable quantity. Number goes with countable nouns (things you can count one by one), not with bulk resources like water or land. Quantity can work with uncountables, but in natural English, amount is the more idiomatic choice for a general measure of such resources. Total would put emphasis on the whole sum and sounds less natural in this context. So the phrase fits best as “a limited amount of land and water.”