A reference question is usually a pronoun, which is highlighted in the passage. You are asked what the highlighted word refers to. If it’s a pronoun then you need to identify what word the pronoun is replacing.
Many millions of years after ferns evolved (but long before the Hawaiian Islands were born from the sea), another kind of flora evolved on Earth: the seed-bearing plants. This was a wonderful biological invention. The seed has an outer coating that surrounds the genetic material of the new plant, and inside this covering is a concentrated supply of nutrients. Thus the seed’s chances of survival are greatly enhanced over those of the naked spore.
The word “This” in paragraph 2 refers to:
- the spread of ferns and mosses in Hawaii
- the creation of the Hawaiian Islands
- the evolution of ferns
- the development of plants that produce seeds
The pronoun “This” refers to the idea of the previous sentence. The previous sentence is “another kind of flora evolved on Earth: the seed-bearing plants”, So, “This was a wonderful biological invention refers to “the seed bearing plans”. So, answer is (D).