SAT English Practice Question

A certain type of algae, called *Chondrus crispus,* is found in cold, rocky marine environments. It is a crucial source of *carrageenan,* a substance commonly used as a thickener in foods like ice cream. In 2022, researchers at the University of California, San Diego, noted that populations of *C. crispus* in the state are declining. The reasons for this decline are unclear, but the researchers suggested that human activity may be a factor. The population of *C. crispus* was much higher in the 1990s than it is today. It was not until recent years that they noticed a change in the population of the algae. The decline in algae populations is not necessarily the result of human activity. The researchers are looking at other possible explanations for this decline. The researchers hope to identify the root cause of the decline by studying the algae over time. What is the main idea of the passage?

1. A.The reasons for the decline in populations of *Chondrus crispus* are unclear, but the researchers have identified human activity as the root cause of the decline.
2. B.The decline in populations of *Chondrus crispus* is not necessarily the result of human activity, but the researchers are looking at other possible explanations for this decline.
3. C.The decline in populations of *Chondrus crispus* may be the result of human activity, but the researchers are unsure about the root cause of the decline.
4. D.The researchers are unsure about the reasons for the decline in populations of *Chondrus crispus*, but they hope to identify the root cause of the decline by studying the algae over time.