Rearrange the following sentences in the proper sequence to form a meaningful paragraph; then answer the questions given below them.

(A) He discovered many patients were diagnosed before turning 65.
(B) Recently, scientists found a genetic marker tied to early-onset Alzheimer’s.
(C) Alzheimer’s is a brain disorder that damages memory and thinking over time.
(D) Using this lead, Rohan studied data from 48 states in the USA.
(E) This result points to the need for early detection and preventive therapy.
(F) This gradual decline is made worse because most treatments only manage symptoms.

Which of the following should be the FOURTH sentence after rearrangement?

To determine the correct sequence of the sentences, let us analyze the logical links between them:

1. Sentence (C) serves as the best opening sentence because it introduces the central topic: "Alzheimer’s is a brain disorder that damages memory and thinking over time."
2. Sentence (F) directly follows (C), as "This gradual decline" refers to the damage to memory and thinking over time mentioned in (C): "This gradual decline is made worse because most treatments only manage symptoms."
3. Sentence (B) introduces a new scientific development related to the disorder: "Recently, scientists found a genetic marker tied to early-onset Alzheimer’s."
4. Sentence (D) logical connects to (B) because it refers to the genetic marker as "this lead" and introduces Rohan: "Using this lead, Rohan studied data from 48 states in the USA."
5. Sentence (A) follows (D) by using the pronoun "He" to refer to Rohan and describing the findings from his study of the data: "He discovered many patients were diagnosed before turning 65."
6. Sentence (E) concludes the paragraph by discussing the implications of Rohan's findings ("This result"): "This result points to the need for early detection and preventive therapy."

Thus, the complete logical sequence of the paragraph is C - F - B - D - A - E.

The fourth sentence in this sequence is D.