Meaning: 'Feat' means an impressive achievement or accomplishment, particularly one that requires skill or effort.

Wrong options:

• feast: A 'feast' refers to a large meal or celebration, which does not fit the context of an achievement related to scientific methods.
• feature: A 'feature' is a distinctive attribute or aspect, but it does not convey the sense of an impressive achievement as 'feat' does.
• faint: 'Faint' means weak or barely perceptible, which is unrelated to the context of a significant achievement.

Correct answer: sequenced

Explanation: The verb 'sequenced' is the past tense of 'sequence,' meaning to arrange in a specific order, which is appropriate in the context of analyzing the Neanderthal genome. It fits grammatically as the main verb of the sentence, indicating the action taken by Pääbo's lab.

Meaning: 'Sequenced' means to determine the order of nucleotides in a DNA molecule, which is a crucial step in genetic analysis.

Wrong options:

• sympathized: 'Sympathized' means to share feelings or emotions, which does not relate to the scientific action of analyzing DNA.
• disturbed: 'Disturbed' implies causing disruption or trouble, which is not relevant to the context of sequencing DNA.
• regulated: 'Regulated' means controlled or maintained, which does not accurately describe the action of sequencing.

Correct answer: tease

Explanation: The verb 'tease' in this context means to gradually reveal or extract information, which fits well with the idea of uncovering secrets from DNA. It is grammatically correct as it follows the auxiliary verb 'has' and aligns with the ongoing nature of paleogenetic research.

Meaning: 'Tease' means to draw out or reveal something gradually, often in a playful or intriguing manner.

Wrong options:

• lease: 'Lease' refers to a contract for renting property, which is unrelated to the context of revealing information from DNA.
• grease: 'Grease' means to lubricate or make slippery, which does not fit the context of extracting secrets from DNA.
• release: 'Release' means to set free or allow to escape, which does not convey the gradual uncovering implied by 'tease'.

Correct answer: course

Explanation: The noun 'course' refers to a direction or path taken, which is appropriate in the context of how the Black Death shifted the trajectory of human history. It fits grammatically as the subject of the sentence and aligns with the historical context being discussed.

Meaning: 'Course' means the direction or path along which something moves or progresses, particularly in a historical context.

Wrong options:

• geek: 'Geek' refers to a person with an eccentric interest, which does not fit the context of historical change.
• contour: 'Contour' refers to the outline or shape of something, which is not relevant to the idea of a historical path or direction.
• discourse: 'Discourse' refers to written or spoken communication, which does not accurately describe the shift in human history.

Correct answer: genetic

Explanation: The adjective 'genetic' relates to genes or heredity, which is fitting in the context of identifying differences that helped people survive the plague. It fits grammatically as a descriptor for 'differences' and aligns with the scientific focus of the study.

Meaning: 'Genetic' means relating to genes or heredity, particularly in the context of biological traits and characteristics.

Wrong options:

• physical: 'Physical' refers to the body or material aspects, which does not specifically address the hereditary differences relevant to survival.
• social: 'Social' pertains to society or community interactions, which is not the focus of the genetic analysis discussed.
• mental: 'Mental' relates to the mind or cognitive processes, which does not fit the context of biological differences related to survival.